CHAPTER XXV.

THE ALIMENTARY CANAL AND ITS APPENDAGES, IN THE CHORDATA.

The alimentary canal in the Chordata is always formed of three sections, analogous to those so universally present in the Invertebrata. These sections are (1) the mesenteron lined by hypoblast; (2) the stomodæum or mouth lined by epiblast, and (3) the proctodæum or anal section lined like the stomodæum by epiblast.

_Mesenteron._

The early development of the epithelial wall of the mesenteron has already been described (Chapter XI.). It forms at first a simple hypoblastic tube extending from near the front end of the body, where it terminates blindly, to the hinder extremity where it is united with the neural tube by the neurenteric canal (fig. 420, _ne_). It often remains for a long time widely open in the middle towards the yolk-sack.

It has already been shewn that from the dorsal wall of the mesenteron the notochord is separated off nearly at the same time as the lateral plates of mesoblast (pp. 292-300).

The subnotochordal rod. At a period slightly subsequent to the formation of the notochord, and before any important differentiations in the mesenteron have become apparent, a remarkable rod-like body, which was first discovered by Götte, becomes split off from the dorsal wall of the alimentary tract in all the Ichthyopsida. This body, which has a purely provisional existence, is known as the subnotochordal rod.

It develops in Elasmobranch embryos in two sections, one situated in the head, and the other in the trunk.

The section in the trunk is the first to appear. The wall of the alimentary canal becomes thickened along the median dorsal line (fig. 412, _x_), or else produced into a ridge into which there penetrates a narrow prolongation of the lumen of the alimentary canal. In either case the cells at the extreme summit become gradually constricted off as a rod, which lies immediately dorsal to the alimentary tract, and ventral to the notochord (fig. 413, _x_).

[FIG. 412. TRANSVERSE SECTION THROUGH THE TAIL REGION OF A PRISTIURUS EMBRYO OF THE SAME AGE AS FIG. 28 E.

_df._ dorsal fin; _sp.c._ spinal cord; _pp._ body cavity; _sp._ splanchnic layer of mesoblast; _so._ somatic layer of mesoblast; _mp´._ portion of splanchnic mesoblast commencing to be differentiated into muscles; _ch._ notochord; _x._ subnotochordal rod arising as an outgrowth of the dorsal wall of the alimentary tract; _al._ alimentary tract.]

[FIG. 413. TRANSVERSE SECTION THROUGH THE TRUNK OF AN EMBRYO SLIGHTLY OLDER THAN FIG. 28 E.

_nc._ neural canal; _pr._ posterior root of spinal nerve; _x._ subnotochordal rod; _ao._ aorta; _sc._ somatic mesoblast; _sp._ splanchnic mesoblast; _mp._ muscle-plate; _mp´._ portion of muscle-plate converted into muscle; _Vv._ portion of the vertebral plate which will give rise to the vertebral bodies; _al._ alimentary tract.]

In the hindermost part of the body its mode of formation differs somewhat from that above described. In this part the alimentary wall is very thick, and undergoes no special growth prior to the formation of the subnotochordal rod; on the contrary, a small linear portion of the wall becomes scooped out along the median dorsal line, and eventually separates from the remainder as the rod in question. In the trunk the splitting off of the rod takes place from before backwards, so that the anterior part of it is formed before the posterior.

The section of the subnotochordal rod in the head would appear to develop in the same way as that in the trunk, and the splitting off from the throat proceeds from before backwards.

On the formation of the dorsal aorta, the subnotochordal rod becomes separated from the wall of the gut and the aorta interposed between the two (fig. 367, _x_).

When the subnotochordal rod attains its fullest development it terminates anteriorly some way in front of the auditory vesicle, though a little behind the end of the notochord; posteriorly it extends very nearly to the extremity of the tail _and is almost co-extensive with the postanal section of the alimentary tract_, though it does not reach quite so far back as the caudal vesicle (fig. 424, _b x_). Very shortly after it has attained its maximum size it begins to atrophy in front. We may therefore conclude that its atrophy, like its development, takes place from before backwards. During the later embryonic stages not a trace of it is to be seen. It has also been met with in Acipenser, Lepidosteus, the Teleostei, Petromyzon, and the Amphibia, in all of which it appears to develop in fundamentally the same way as in Elasmobranchii. In Acipenser it appears to persist in the adult as the subvertebral ligament (Bridge, Salensky). It has not yet been found in a fully developed form in any amniotic Vertebrate, though a thickening of the hypoblast, which may perhaps be a rudiment of it, has been found by Marshall and myself in the Chick (fig. 110, _x_).

Eisig has instituted an interesting comparison between it and an organ which he has found in a family of Chætopods, the Capitellidæ. In these forms there is a tube underlying the alimentary tract for nearly its whole length, and opening into it in front, and probably behind. A remnant of such a tube might easily form a rudiment like the subnotochordal rod of the Ichthyopsida, and as Eisig points out the prolongation into the latter during its formation of the lumen of the alimentary tract distinctly favours such a view of its original nature. We can however hardly suppose that there is any direct genetic connection between Eisig's organ in the Capitellidæ and the subnotochordal rod of the Chordata.

Splanchnic mesoblast and mesentery. The mesenteron consists at first of a simple hypoblastic tube, which however becomes enveloped by a layer of splanchnic mesoblast. This layer, which is not at first continued over the dorsal side of the mesenteron, gradually grows in, and interposes itself between the hypoblast of the mesenteron, and the organs above. At the same time it becomes differentiated into two layers, viz. an outer epithelioid layer which gives rise to part of the peritoneal epithelium, and an inner layer of undifferentiated cells which in time becomes converted into the connective tissue and muscular walls of the mesenteron. The connective tissue layers become first formed, while of the muscular layers the circular is the first to make its appearance.

Coincidently with their differentiation the connective tissue stratum of the peritoneum becomes established.

_The Mesentery._ Prior to the splanchnic mesoblast growing round the alimentary tube above, the attachment of the latter structure to the dorsal wall of the body is very wide. On the completion of this investment the layer of mesoblast suspending the alimentary tract becomes thinner, and at the same time the alimentary canal appears to be drawn downwards and away from the vertebral column.

In what may be regarded as the thoracic division of the general pleuroperitoneal space, along that part of the alimentary canal which will form the oesophagus, this withdrawal is very slight, but it is very marked in the abdominal region. In the latter the at first straight digestive canal comes to be suspended from the body above by a narrow flattened band of mesoblastic tissue. This flattened band is the _mesentery_, shewn commencing in fig. 117, and much more advanced in fig. 119, _M_. It is covered on either side by a layer of flat cells, which form part of the general peritoneal epithelioid lining, while its interior is composed of indifferent tissue.

The primitive simplicity in the arrangement of the mesentery is usually afterwards replaced by a more complicated disposition, owing to the subsequent elongation and consequent convolution of the intestine and stomach.

The layer of peritoneal epithelium on the ventral side of the stomach is continued over the liver, and after embracing the liver, becomes attached to the ventral abdominal wall (fig. 380). Thus in the region of the liver the body cavity is divided into two halves by a membrane, the two sides of which are covered by the peritoneal epithelium, and which encloses the stomach dorsally and the liver ventrally. The part of the membrane between the stomach and liver is narrow, and constitutes a kind of mesentery suspending the liver from the stomach: it is known to human anatomists as the lesser omentum.

The part of the membrane connecting the liver with the anterior abdominal wall constitutes the falciform or suspensory ligament of the liver. It arises by a secondary fusion, and is not a remnant of a primitive ventral mesentery (_vide_ pp. 624 and 625).

The mesentery of the stomach, or mesogastrium, enlarges in Mammalia to form a peculiar sack known as the greater omentum.

The mesenteron exhibits very early a trifold division. An anterior portion, extending as far as the stomach, becomes separated off as the respiratory division. On the formation of the anal invagination the portion of the mesenteron behind the anus becomes marked off as the postanal division, and between the postanal section and the respiratory division is a middle portion forming an intestinal and cloacal division.

_The respiratory division of the mesenteron._

This section of the alimentary canal is distinguished by the fact that its walls send out a series of paired diverticula, which meet the skin, and after a perforation has been effected at the regions of contact, form the branchial or visceral clefts.

In Amphioxus the respiratory region extends close up to the opening of the hepatic diverticulum, and therefore to a position corresponding with the commencement of the intestine in higher types. In the craniate Vertebrata the number of visceral clefts has become reduced, but from the extension of the visceral clefts in Amphioxus, combined with the fact that in the higher Vertebrata the vagus nerve, which is essentially the nerve of the branchial pouches, supplies in addition the walls of the oesophagus and stomach, it may reasonably be concluded, as has been pointed out by Gegenbaur, that the true respiratory region primitively included the region which in the higher types forms the oesophagus and stomach.

In Ascidians the respiratory sack is homologous with the respiratory tract of Amphioxus.

The details of the development of the branchial clefts in the different groups of Vertebrata have already been described in the systematic part of this work.

In all the Ichthyopsida the walls of a certain number of clefts become folded; and in the mesoblast within these folds a rich capillary network, receiving its blood from the branchial arteries, becomes established. These folds constitute the true internal gills.

In addition to internal gills _external branchial processes_ covered by epiblast are placed on certain of the visceral arches in the larva of Polypterus, Protopterus and many Amphibia. The external gills have probably no genetic connection with the internal gills.

The so-called external gills of the embryos of Elasmobranchii are merely internal gills prolonged outwards through the gill clefts.

The posterior part of the primitive respiratory division of the mesenteron becomes, in all the higher Vertebrata, the oesophagus and stomach. With reference to the development of these parts the only point worth especially noting is the fact that in Elasmobranchii and Teleostei their lumen, though present in very young embryos, becomes at a later stage completely filled up, and thus the alimentary tract in the regions of the oesophagus and stomach becomes a solid cord of cells (fig. 23 A, _oes_): as already suggested (p. 61) it seems not impossible that this feature may be connected with the fact that the oesophageal region of the throat was at one time perforated by gill clefts.

In addition to the gills two important organs, viz. the thyroid body and the lungs, take their origin from the respiratory region of the alimentary tract.

[FIG. 414. DIAGRAMMATIC VERTICAL SECTION OF A JUST-HATCHED LARVA OF PETROMYZON. (From Gegenbaur; after Calberla.)

_o._ mouth; _o´._ olfactory pit; _v._ septum between stomodæum and mesenteron; _h._ thyroid involution; _n._ spinal cord; _ch._ notochord; _c._ heart; _a._ auditory vesicle.]

Thyroid body. In the Ascidians the origin of a groove-like diverticulum of the ventral wall of the branchial sack, bounded by two lateral folds, and known as the endostyle or hypopharyngeal groove, has already been described (p. 18). This groove remains permanently open to the pharyngeal sack, and would seem to serve as a glandular organ secreting mucus. As was first pointed out by W. Müller there is present in Amphioxus a very similar and probably homologous organ, known as the hypopharyngeal groove.

[FIG. 415. DIAGRAMMATIC TRANSVERSE SECTIONS THROUGH THE BRANCHIAL REGION OF YOUNG LARVÆ OF PETROMYZON. (From Gegenbaur; after Calberla.)

_d._ branchial region of throat.]

In the higher Vertebrata this organ never retains its primitive condition in the adult state. In the larva of Petromyzon there is, however, present a ventral groove-like diverticulum of the throat, extending from about the second to the fourth visceral cleft. This organ is shewn in longitudinal section in fig. 414, _h_, and in transverse section in fig. 415, and has been identified by W. Müller (Nos. 565 and 566) with the hypopharyngeal groove of Amphioxus and Ascidians. It does not, however, long retain its primitive condition, but its opening becomes gradually reduced to a pore, placed between the third and fourth of the permanent clefts (fig. 416, _th_). This opening is retained throughout the Ammocoete condition, but the organ becomes highly complicated, with paired anterior and posterior horns and a median spiral portion. In the adult the connection with the pharynx is obliterated, and the organ is partly absorbed and partly divided up into a series of glandular follicles, and eventually forms _the thyroid body_.

From the consideration of the above facts W. Müller was led to the conclusion _that the thyroid body of the Craniata was derived from the endostyle or hypopharyngeal groove_. In all the higher Vertebrata the thyroid body arises as a diverticulum of the ventral wall of the throat in the region either of the mandibular or hyoid arches (fig. 417, _Th_), which after being segmented off becomes divided up into follicles.

In Elasmobranch embryos it appears fairly early as a diverticulum from the ventral surface of the throat in the region of the _mandibular arch_, extending from the border of the mouth to the point where the ventral aorta divides into the two aortic branches of the mandibular arch (fig. 417, _Th_). Somewhat later it becomes in Scyllium and Torpedo solid, though still retaining its attachment to the wall of the oesophagus. It continues to grow in length, and becomes divided up into a number of solid branched lobules separated by connective tissue septa. Eventually its connection with the throat becomes lost, and the lobules develop a lumen. In Acanthias the lumen of the gland is retained (W. Müller) till after its detachment from the throat. It preserves its embryonic position through life. In Amphibia it originates, as in Elasmobranchii, from the region of the mandibular arch; but when first visible it forms a double epithelial wall connecting the throat with the nervous layer of the epidermis. It subsequently becomes detached from the epidermis, and then has the usual form of a diverticulum from the throat. In most Amphibians it becomes divided into two lobes, and so forms a paired body. The peculiar connection between the thyroid diverticulum and the epidermis in Amphibia has been noted by Götte in Bombinator, and by Scott and Osborn in Triton. It is not very easy to see what meaning this connection can have.

[FIG. 416. DIAGRAMMATIC VERTICAL SECTION THROUGH THE HEAD OF A LARVA OF PETROMYZON.

The larva had been hatched three days, and was 4.8 mm. in length. The optic and auditory vesicles are supposed to be seen through the tissues. The letter _tv_ pointing to the base of the velum is where Scott believes the hyomandibular cleft to be situated.

_c.h._ cerebral hemisphere; _th._ optic thalamus; _in._ infundibulum; _pn._ pineal gland; _mb._ mid-brain; _cb._ cerebellum; _md._ medulla oblongata; _au.v._ auditory vesicle; _op._ optic vesicle; _ol._ olfactory pit; _m._ mouth; _br.c._ branchial pouches; _th._ thyroid involution; _v.ao._ ventral aorta; _ht._ ventricle of heart; _ch._ notochord.]

In the Fowl (W. Müller) the thyroid body arises at the end of the second or beginning of the third day as an outgrowth from the hypoblast of the throat, opposite the point of origin of the anterior arterial arch. This outgrowth becomes by the fourth day a solid mass of cells, and by the fifth ceases to be connected with the epithelium of the throat, becoming at the same time bilobed. By the seventh day it has travelled somewhat backwards, and the two lobes have completely separated from each other. By the ninth day the whole is invested by a capsule of connective tissue, which sends in septa dividing it into a number of lobes or solid masses of cells, and by the sixteenth day it is a paired body composed of a number of hollow branched follicles, each with a 'membrana propria,' and separated from each other by septa of connective tissue. It finally travels back to the point of origin of the carotids.

[FIG. 417. SECTION THROUGH THE HEAD OF AN ELASMOBRANCH EMBRYO, AT THE LEVEL OF THE AUDITORY INVOLUTION.

_Th._ rudiment of thyroid body; _aup._ auditory pit; _aun._ ganglion of auditory nerve; _iv.v._ roof of fourth ventricle; _a.c.v._ anterior cardinal vein; _aa._ aorta; _I.aa._ aortic trunk of mandibular arch; _pp._ head cavity of mandibular arch; _Ivc._ alimentary pouch which will form the first visceral cleft.]

Amongst Mammalia the thyroid arises in the Rabbit (Kölliker) and Man (His) as a hollow diverticulum of the throat at the bifurcation of the foremost pair of aortic arches. It soon however becomes solid, and is eventually detached from the throat and comes to lie on the ventral side of the larynx or windpipe. The changes it undergoes are in the main similar to those in the lower Vertebrata. It becomes partially constricted into two lobes, which remain however united by an isthmus[278]. The fact that the thyroid sometimes arises in the region of the first and sometimes in that of the second cleft is probably to be explained by its rudimentary character.

[278] Wölfler (No. 571) states that in the Pig and Calf the thyroid body is formed as a pair of epithelial vesicles, which are developed as outgrowths of the walls of the first pair of visceral clefts. He attempts to explain the contradictory observations of other embryologists by supposing that they have mistaken the ventral ends of visceral pouches for an unpaired outgrowth of the throat. Stieda (No. 569) also states that in the Pig and Sheep the thyroid arises as a paired body from the epithelium of a pair of visceral clefts, at a much later period than would appear from the observations of His and Kölliker. In view of the comparative development of this organ it is difficult to accept either Wölfler's or Stieda's account. Wölfler's attempt to explain the supposed errors of his predecessors is certainly not capable of being applied in the case of Elasmobranch Fishes, or of Petromyzon; and I am inclined to think that the method of investigation by transverse sections, which has been usually employed, is less liable to error than that by longitudinal sections which he has adopted.

The Thymus gland. The thymus gland may conveniently be dealt with here, although its origin is nearly as obscure as its function. It has usually been held to be connected with the lymphatic system. Kölliker was the first to shew that this view was probably erroneous, and he attempted to prove that it was derived in the Rabbit from the walls of one of the visceral clefts, mainly on the ground of its presenting in the embryo an epithelial character.

Stieda (No. 569) has recently verified Kölliker's statements. He finds that in the Pig and the Sheep the thymus arises as a paired outgrowth from the epithelial remnants of a pair of visceral clefts. Its two lobes may at first be either hollow (Sheep) or solid (Pig), but eventually become solid, and unite in the median line. Stieda and His hold that in the adult gland, the so-called corpuscles of Hassall are the remnants of the embryonic epithelial part of the gland, and that the lymphatic part of it is of mesoblastic origin; but Kölliker believes the lymphatic cells to be direct products of the embryonic epithelial cells.

The posterior visceral clefts in the course of their atrophy give rise to various more or less conspicuous bodies of a pseudo-glandular nature, which have been chiefly studied by Remak[279].

[279] For details on these organs _vide_ Kölliker, _Entwicklungsgeschichte_, p. 881.

Swimming bladder and lungs. A swimming bladder is present in all Ganoids and in the vast majority of Teleostei. Its development however is only imperfectly known.

In the Salmon and Carp it arises, as was first shewn by Von Baer, as an outgrowth of the alimentary tract, shortly in front of the liver. In these forms it is at first placed on the dorsal side and slightly to the right, and grows backwards on the dorsal side of the gut, between the two folds of the mesentery.

The absence of a pneumatic duct in the Physoclisti would appear to be due to a post-larval atrophy.

In Lepidosteus the air-bladder appears to arise, as in the Teleostei, as an invagination of the dorsal wall of the oesophagus.

In advanced embryos of Galeus, Mustelus and Acanthias, Miklucho-Maclay detected a small diverticulum opening on the dorsal side of the oesophagus, which he regards as a rudiment of a swimming bladder. This interpretation must however be regarded as somewhat doubtful.

_The lungs._ The lungs originate in a nearly identical way in all the Vertebrate forms in which their development has been observed. They are essentially buds or processes of the ventral wall of the primitive oesophagus.

At a point immediately behind the region of the visceral clefts the cavity of the alimentary canal becomes compressed laterally, and at the same time constricted in the middle, so that its transverse section (fig. 418 1) is somewhat hourglass-shaped, and shews an upper or dorsal chamber _d_, joining on to a lower or ventral chamber _l_ by a short narrow neck.

The hinder end of the lower tube enlarges (fig. 418 2), and then becomes partially divided into two lobes (fig. 418 3). All these parts at first freely communicate, but the two lobes, partly by their own growth, and partly by a process of constriction, soon become isolated posteriorly; while in front they open into the lower chamber of the oesophagus (fig. 422).

[FIG. 418. FOUR DIAGRAMS ILLUSTRATING THE FORMATION OF THE LUNGS. (After Götte.)

_a._ mesoblast; _b._ hypoblast; _d._ cavity of digestive canal; _l._ cavity of the pulmonary diverticulum.

In (1) the digestive canal has commenced to be constricted into an upper and lower canal; the former the true alimentary canal, the latter the pulmonary tube; the two tubes communicate with each other in the centre. In (2) the lower (pulmonary) tube has become expanded. In (3) the expanded portion of the tube has become constricted into two tubes, still communicating with each other and with the digestive canal. In (4) these are completely separated from each other and from the digestive canal, and the mesoblast has also begun to exhibit externally changes corresponding to the internal changes which have been going on.]

By a continuation forwards of the process of constriction the lower chamber of the oesophagus, carrying with it the two lobes above mentioned, becomes gradually transformed into an independent tube, opening in front by a narrow slit-like aperture into the oesophagus. The single tube in front is the rudiment of the trachea and larynx, while the two diverticula behind become (fig. 419, _lg_) the bronchial tubes and lungs.

While the above changes are taking place in the hypoblastic walls of the alimentary tract, the splanchnic mesoblast surrounding these structures becomes very much thickened; but otherwise bears no marks of the internal changes which are going on, so that the above formation of the lungs and trachea cannot be seen from the surface. As the paired diverticula of the lungs grow backwards, the mesoblast around them takes however the form of two lobes, into which they gradually bore their way.

There do not seem to be any essential differences in the mode of formation of the above structures in the types so far observed, viz. Amphibia, Aves and Mammalia. Writers differ as to whether the lungs first arise as paired diverticula, or as a single diverticulum; and as to whether the rudiments of the lungs are established before those of the trachea. If the above account is correct it would appear that any of these positions might be maintained. Phylogenetically interpreted the ontogeny of the lungs appears however to imply that this organ was first an unpaired structure and has become secondarily paired, and that the trachea was relatively late in appearing.

[FIG. 419. SECTION THROUGH THE CARDIAC REGION OF AN EMBRYO OF LACERTA MURALIS OF 9 MM. TO SHEW THE MODE OF FORMATION OF THE PERICARDIAL CAVITY.

_ht._ heart; _pc._ pericardial cavity; _al._ alimentary tract; _lg._ lung; _l._ liver; _pp._ body cavity; _md._ open end of Müllerian duct; _wd._ Wolffian duct; _vc._ vena cava inferior; _ao._ aorta; _ch._ notochord; _mc._ medullary cord.]

The further development of the lungs is at first, in the higher types at any rate, essentially similar to that of a racemose gland. From each primitive diverticulum numerous branches are given off. In Aves and Mammalia (fig. 355) they are mainly confined to the dorsal and lateral parts. These branches penetrate into the surrounding mesoblast and continue to give rise to secondary and tertiary branches. In the mesoblast around them numerous capillaries make their appearance, and the further growth of the bronchial tubes is supposed by Boll to be due to the mutual interaction of the hitherto passive mesoblast and of the hypoblast.

The further changes in the lungs vary somewhat in the different forms.

The air sacks are the most characteristic structures of the avian lung. They are essentially the dilated ends of the primitive diverticula or of their main branches.

In Mammalia (Kölliker, No. 298) the ends of the bronchial tubes become dilated into vesicles, which may be called the primary air-cells. At first, owing to their development at the ends of the bronchial branches, these are confined to the surface of the lungs. At a later period the primary air-cells divide each into two or three parts, and give rise to secondary air-cells, while at the same time the smallest bronchial tubes, which continue all the while to divide, give rise at all points to fresh air-cells. Finally the bronchial tubes cease to become more branched, and the air-cells belonging to each minute lobe come in their further growth to open into a common chamber. Before the lungs assume their function the embryonic air-cells undergo a considerable dilatation.

_The trachea and larynx._ The development of the trachea and larynx does not require any detailed description. The larynx is formed as a simple dilatation of the trachea. The cartilaginous structures of the larynx are of the same nature as those of the trachea.

It follows from the above account that the whole pulmonary structure is the result of the growth by budding of a system of branched hypoblastic tubes in the midst of a mass of mesoblastic tissue, the hypoblastic elements giving rise to the epithelium of the tubes, and the mesoblast providing the elastic, muscular, cartilaginous, vascular, and other connective tissues of the tracheal and bronchial walls.

There can be no doubt that the lungs and air-bladder are homologous structures, and the very interesting memoir of Eisig on the air-bladder of the Chætopoda[280] shews it to be highly probable that they are the divergent modifications of a primitive organ, which served as a reservoir for gas secreted in the alimentary tract, the gas in question being probably employed for respiration when, for any reason, ordinary respiration by the gills was insufficient.

[280] H. Eisig, "Ueb. d. Vorkommen eines schwimmblasenähnlichen Organs bei Anneliden." _Mittheil. a. d. zool. Station z. Neapel_, Vol. II. 1881.

Such an organ might easily become either purely respiratory, receiving its air from the exterior, and so form a true lung; or mainly hydrostatic, forming an air-bladder, as in Ganoidei and Teleostei.

It is probable that in the Elasmobranchii the air-bladder has become aborted, and the organ discovered by Micklucho-Maclay may perhaps be a last remnant of it.

The middle division of the mesenteron. The middle division of the mesenteron, forming the intestinal and cloacal region, is primitively a straight tube, the intestinal region of which in most Vertebrate embryos is open below to the yolk-sack.

Cloaca. In the Elasmobranchii, the embryos of which probably retain a very primitive condition of the mesenteron, this region is not at first sharply separated from the postanal section behind. Opposite the point where the anus will eventually appear a dilatation of the mesenteron arises, which comes in contact with the external skin (fig. 28 E, _an_). This dilatation becomes the hypoblastic section of the cloaca. It communicates behind with the postanal gut (fig. 424 D), and in front with the intestine; and _may be defined as the dilated portion of the alimentary tract which receives the genital and urinary ducts and opens externally by the proctodæum_.

In Acipenser and Amphibia the cloacal region is indicated as a ventral diverticulum of the mesenteron even before the closure of the blastopore. It is shewn in the Amphibia at an early stage in fig. 73, and at a later period, when in contact with the skin at the point where the anal invagination is about to appear, in fig. 420.

[FIG. 420. LONGITUDINAL SECTION THROUGH AN ADVANCED EMBRYO OF BOMBINATOR. (After Götte.)

_m._ mouth; _an._ anus; _l._ liver; _ne._ neurenteric canal; _mc._ medullary canal; _ch._ notochord; _pn._ pineal gland.]

In the Sauropsida and Mammalia the cloaca appears as a dilatation of the mesenteron, which receives the opening of the allantois almost as soon as the posterior part of the mesenteron is established.

The eventual changes which it undergoes have been already dealt with in connection with the urinogenital organs.

Intestine. The region in front of the cloaca forms the intestine. In certain Vertebrata it nearly retains its primitive character as a straight tube; and in these types its anterior part is characterised by the presence of a peculiar fold, which in a highly specialised condition is known as the spiral valve. This structure appears in its simplest form in Ammocoetes. It there consists of a fold in the wall of the intestine, giving to the lumen of this canal a semilunar form in section, and taking a half spiral.

In Elasmobranchii a similar fold to that in Ammocoetes first makes its appearance in the embryo. This fold is from the first not quite straight, but winds in a long spiral round the intestine. In the course of development it becomes converted into a strong ridge projecting into the lumen of the intestine (fig. 388, _l_). The spiral it makes becomes much closer, and it thus acquires the form of the adult spiral valve. A spiral valve is also found in Chimæra and Ganoids. No rudiment of such an organ is found in the Teleostei, the Amphibia, or the higher Vertebrata.

The presence of this peculiar organ appears to be a very primitive Vertebrate character. The intestine of Ascidians exhibits exactly the same peculiarity as that of Ammocoetes, and we may probably conclude from embryology that the ancestral Chordata were provided with a straight intestine having a fold projecting into its lumen, to increase the area of the intestinal epithelium.

In all forms in which there is not a spiral valve, with the exception of a few Teleostei, the intestine becomes considerably longer than the cavity which contains it, and therefore necessarily more or less convoluted.

The posterior part usually becomes considerably enlarged to form the rectum or in Mammalia the large intestine.

In Elasmobranchii there is a peculiar gland opening into the dorsal side of the rectum, and in many other forms there is a cæcum at the commencement of the rectum or of the large intestine.

In Teleostei, the Sturgeon and Lepidosteus there opens into the front end of the intestine a number of cæcal pouches known as the pancreatic cæca. In the adult Sturgeon these pouches unite to form a compact gland, but in the embryo they arise as a series of isolated outgrowths of the duodenum.

Connected with the anterior portion of the middle region of the alimentary canal, which may be called the duodenum, are two very important and constant glandular organs, the liver and the pancreas.

The liver. The liver is the earliest formed and largest glandular organ in the embryo.

It appears in its simplest form in Amphioxus as a single unbranched diverticulum of the alimentary tract, immediately behind the respiratory region, which is directed forwards and placed on the left side of the body.

[FIG. 421. SECTION THROUGH THE VENTRAL PART OF THE TRUNK OF A YOUNG EMBRYO OF SCYLLIUM AT THE LEVEL OF THE UMBILICAL CORD.

_b._ pectoral fin; _ao._ dorsal aorta; _cav._ cardinal vein; _ua._ vitelline artery; _uv._ vitelline vein united with subintestinal vein; _al._ duodenum; _l._ liver; _sd._ opening of segmental duct into the body-cavity; _mp._ muscle-plate; _um._ umbilical canal.]

In all true Vertebrata the gland has a much more complicated structure. It arises as a ventral outgrowth of the duodenum (fig. 420, _l_). This outgrowth may be at first single, and then grow out into two lobes, as in Elasmobranchii (fig. 421) and Amphibia, or have from the first the form of two somewhat unequal diverticula, as in Birds (fig. 422), or again as in the Rabbit (Kölliker) one diverticulum may be first formed, and a second one appear somewhat later. The hepatic diverticula, whatever may be their primitive form, grow into a special thickening of the splanchnic mesoblast.

From the primitive diverticula there are soon given off a number of hollow buds (fig. 421) which rapidly increase in length and number, and form the so-called hepatic cylinders. They soon anastomose and unite together, and so constitute an irregular network. Coincidently with the formation of the hepatic network the united vitelline and visceral vein or veins (_u.v_), in their passage through the liver, give off numerous branches, and gradually break up into a plexus of channels which form a secondary network amongst the hepatic cylinders. In Amphibia these channels are stated by Götte to be lacunar, but in Elasmobranchii, and probably Vertebrata generally, they are from the first provided with distinct though delicate walls.

It is still doubtful whether the hepatic cylinders are as a rule hollow or solid. In Elasmobranchii they are at first provided with a large lumen, which though it becomes gradually smaller never entirely vanishes. The same seems to hold good for Amphibia and some Mammalia. In Aves the lumen of the cylinders is even from the first much more difficult to see, and the cylinders are stated by Remak to be solid, and he has been followed in this matter by Kölliker. In the Rabbit also Kölliker finds the cylinders to be solid.

The embryonic hepatic network gives rise to the parenchyma of the adult liver, with which in its general arrangement it closely agrees. The blood-channels are at first very large, and have a very irregular arrangement; and it is not till comparatively late that the hepatic lobules with their characteristic vascular structures become established.

[FIG. 422. DIAGRAM OF THE DIGESTIVE TRACT OF A CHICK UPON THE FOURTH DAY. (After Götte.)

The black line indicates the hypoblast. The shaded part around it is the splanchnic mesoblast.

_lg._ lung; _st._ stomach; _p._ pancreas; _l._ liver.]

The biliary ducts are formed either from some of the primitive hepatic cylinders, or, as would seem to be the case in Elasmobranchii and Birds (fig. 422), from the larger diverticula of the two primitive outgrowths.

The gall-bladder is so inconstant, and the arrangement of the ducts opening into the intestine so variable, that no general statements can be made about them. In Elasmobranchii the primitive median diverticulum (fig. 421) gives rise to the ductus choledochus. Its anterior end dilates to form a gall-bladder.

In the Rabbit a ductus choledochus is formed by a diverticulum from the intestine at the point of insertion of the two primitive lobes. The gall-bladder arises as a diverticulum of the right primitive lobe.

The liver is relatively very large during embryonic life and has, no doubt, important functions in connection with the circulation.

The pancreas. So far as is known the development of the pancreas takes place on a very constant type throughout the series of craniate Vertebrata, though absent in some of the Teleostean fishes and Cyclostomata, and very much reduced in most Teleostei and in Petromyzon.

It arises nearly at the same time as the liver in the form of a hollow outgrowth from the dorsal side of the intestine nearly opposite but slightly behind the hepatic outgrowth (fig. 422, _p_). It soon assumes, in Elasmobranchii and Mammalia, somewhat the form of an inverted funnel, and from the expanded dorsal part of the funnel there grow out numerous hollow diverticula into the passive splanchnic mesoblast.

As the ductules grow longer and become branched, vascular processes grow in between them, and the whole forms a compact glandular body in the mesentery on the dorsal side of the alimentary tract. The funnel-shaped receptacle loses its original form, and elongating, assumes the character of a duct.

From the above mode of development it is clear that the glandular cells of the pancreas are derived from the hypoblast.

Into the origin of the varying arrangements of the pancreatic ducts it is not possible to enter in detail. In some cases, _e.g._ the Rabbit (Kölliker), the two lobes and ducts arise from a division of the primitive gland and duct. In other cases, _e.g._ the Bird, a second diverticulum springs from the alimentary tract. In a large number of instances the primitive condition with a single duct is retained.

Postanal section of the mesenteron. In the embryos of all the Chordata there is a section of the mesenteron placed behind the anus. This section invariably atrophies at a comparatively early period of embryonic life; but it is much better developed in the lower forms than in the higher. At its posterior extremity it is primitively continuous with the neural tube (fig. 420), as was first shewn by Kowalevsky.

The canal connecting the neural and alimentary canals has already been described as the neurenteric canal, and represents the remains of the blastopore.

In the Tunicata the section of the mesenteron, which in all probability corresponds to the postanal gut of the Vertebrata, is that immediately following the dilated portion which gives rise to the branchial cavity and permanent intestine. It has already been shewn that from the dorsal and lateral portions of this section of the primitive alimentary tract the notochord and muscles of the Ascidian tadpole are derived. The remaining part of its walls forms a solid cord of cells (fig. 423, _al´_), which either atrophies, or, according to Kowalevsky, gives rise to blood-vessels.

[FIG. 423. TRANSVERSE OPTICAL SECTION OF THE TAIL OF AN EMBRYO OF PHALLUSIA MAMMILLATA. (After Kowalevsky.)

The section is from an embryo of the same age as fig. 8 IV.

_ch._ notochord; _n.c._ neural canal; _me._ mesoblast; _al´._ hypoblast of tail.]

In Amphioxus the postanal gut, though distinctly developed, is not very long, and atrophies at a comparatively early period.

In Elasmobranchii this section of the alimentary tract is very well developed, and persists for a considerable period of embryonic life. The following is a history of its development in the genus Scyllium.

Shortly after the stage when the anus has become marked out by the alimentary tract sending down a papilliform process towards the skin, the postanal gut begins to develop a terminal dilatation or vesicle, connected with the remainder of the canal by a narrower stalk.

The walls both of the vesicle and stalk are formed of a fairly columnar epithelium. The vesicle communicates in front by a narrow passage with the neural canal, and behind is continued into two horns corresponding with the two caudal swellings previously spoken of (p. 55). Where the canal is continued into these two horns, its walls lose their distinctness of outline, and become continuous with the adjacent mesoblast.

In the succeeding stages, as the tail grows longer and longer, the postanal section of the alimentary tract grows with it, without however undergoing alteration in any of its essential characters. At the period of the maximum development, it has a length of about 1/3 of that of the whole alimentary tract.

Its features at a stage shortly before the external gills have become prominent are illustrated by a series of transverse sections through the tail (fig. 424). The four sections have been selected for illustration out of a fairly-complete series of about one hundred and twenty.

Posteriorly (A) there is present a terminal vesicle (_alv_) .25 mm. in diameter, which communicates dorsally by a narrow opening with the neural canal (_nc_); to this is attached a stalk in the form of a tube, also lined by columnar epithelium, and extending through about thirty sections (B _al_). Its average diameter is about .084 mm., and its walls are very thick. Overlying its front end is the subnotochordal rod (_x_), but this does not extend as far back as the terminal vesicle.

The thick-walled stalk of the vesicle is connected with the cloacal section of the alimentary tract by a very narrow thin-walled tube (C _al_). This for the most part has a fairly uniform calibre, and a diameter of not more than .035 mm. Its walls are formed of flattened epithelial cells. At a point not far from the cloaca it becomes smaller, and its diameter falls to .03 mm. In front of this point it rapidly dilates again, and, after becoming fairly wide, opens on the dorsal side of the cloacal section of the alimentary canal just behind the anus (D _al_).

[FIG. 424. FOUR SECTIONS THROUGH THE POSTANAL PART OF THE TAIL OF AN EMBRYO OF THE SAME AGE AS FIG. 28 F.

A. is the posterior section.

_nc._ neural canal; _al._ postanal gut; _alv._ caudal vesicle of postanal gut; _x._ subnotochordal rod; _mp._ muscle-plate; _ch._ notochord; _cl.al._ cloaca; _ao._ aorta; _v.cau._ caudal vein.]

Very shortly after the stage to which the above figures belong, at a point a little behind the anus, where the postanal section of the canal was thinnest in the previous stage, it becomes solid, and a rupture here occurs in it at a slightly later period.

The atrophy of this part of the alimentary tract having once commenced proceeds rapidly. The posterior part first becomes reduced to a small rudiment near the end of the tail. There is no longer a terminal vesicle, nor a neurenteric canal. The portion of the postanal section of the alimentary tract, just behind the cloaca, is for a short time represented by a small rudiment of the dilated part which at an earlier period opened into the cloaca.

In Teleostei the vesicle at the end of the tail, discovered by Kupffer, (fig. 34, _hyv_) is probably the equivalent of the vesicle at the end of the postanal gut in Elasmobranchii.

In Petromyzon and in Amphibia there is a well-developed postanal gut connected with a neurenteric canal which gradually atrophies. It is shewn in the embryo of Bombinator in fig. 420.

[FIG. 425. DIAGRAMMATIC LONGITUDINAL SECTION THROUGH THE POSTERIOR END OF AN EMBRYO BIRD AT THE TIME OF THE FORMATION OF THE ALLANTOIS.

_ep._ epiblast; _Sp.c._ spinal canal; _ch._ notochord; _n.e._ neurenteric canal; _hy._ hypoblast; _p.a.g._ postanal gut; _pr._ remains of primitive streak folded in on the ventral side; _al._ allantois; _me._ splanchnic mesoblast; _an._ point where anus will be formed; _p.c._ perivisceral cavity; _am._ amnion; _so._ somatopleure; _sp._ splanchnopleure.]

Amongst the amniotic Vertebrata the postanal gut is less developed than in the Ichthyopsida. A neurenteric canal is present for a short period in various Birds (Gasser, etc.) and in the Lizard, but disappears very early. There is however, as has been pointed out by Kölliker, a well-marked postanal gut continued as a narrow tube from behind the cloaca into the tail both in the Bird (fig. 425, _p.a.g._) and Mammals (the Rabbit), but especially in the latter. It atrophies early as in lower forms.

The morphological significance of the postanal gut and of the neurenteric canal has already been spoken of in Chapter XII., p. 323.

_The Stomodæum._

The anterior section of the permanent alimentary tract is formed by an invagination of epiblast, constituting a more or less considerable pit, with its inner wall in contact with the blind anterior extremity of the alimentary tract.

In Ascidians this pit is placed on the dorsal surface (fig. 9, _o_), and becomes the permanent oral cavity of these forms. In the larva of Amphioxus it is stated to be formed unsymmetrically (_vide_ p. 5), but further observations on its development are required.

[FIG. 426. LONGITUDINAL SECTION THROUGH THE BRAIN OF A YOUNG PRISTIURUS EMBRYO.

_cer._ unpaired rudiment of the cerebral hemispheres; _pn._ pineal gland; _In._ infundibulum; _pt._ ingrowth from mouth to form the pituitary body; _mb._ mid-brain; _cb._ cerebellum; _ch._ notochord; _al._ alimentary tract; _Iaa._ artery of mandibular arch.]

In the true Vertebrata it is always formed on the ventral surface of the head, immediately behind the level of the fore-brain (fig. 426), and is deeper in Petromyzon (fig. 416, _m_) than in any other known form.

From the primary buccal cavity or stomodæum there grows out the pituitary pit (fig. 426, _pt_), the development of which has already been described (p. 435).

The wall separating the stomodæum from the mesenteron always becomes perforated, usually at an early stage of development, and though in Petromyzon the boundary between the two cavities remains indicated by the velum, yet in the higher Vertebrata all trace of this boundary is lost, and the original limits of the primitive buccal cavity become obliterated; while a secondary buccal cavity, partly lined by hypoblast and partly by epiblast, becomes established.

This cavity, apart from the organs which belong to it, presents important variations in structure. In most Pisces it retains a fairly simple character, but in the Dipnoi its outer boundary becomes extended so as to enclose the ventral opening of the nasal sack, which thenceforward constitutes the posterior nares.

In Amphibia and Amniota the posterior nares also open well within the boundary of the buccal cavity.

In the Amniota further important changes take place.

In the first place a plate grows inwards from each of the superior maxillary processes (fig. 427, _p_), and the two plates, meeting in the middle line, form a horizontal septum dividing the front part of the primitive buccal cavity into a dorsal respiratory section (_n_), containing the opening of the posterior nares, and a ventral cavity, forming the permanent mouth. The two divisions thus formed open into a common cavity behind. The horizontal septum, on the development within it of an osseous plate, constitutes the hard palate.

[FIG. 427. DIAGRAM SHEWING THE DIVISION OF THE PRIMITIVE BUCCAL CAVITY INTO THE RESPIRATORY SECTION ABOVE AND THE TRUE MOUTH BELOW. (From Gegenbaur.)

_p._ palatine plate of superior maxillary process; _m._ permanent mouth; _n._ posterior part of nasal passage; _e._ internasal septum.]

An internasal septum (fig. 427, _e_) may more or less completely divide the dorsal cavity into two canals, continuous respectively with the two nasal cavities.

In Mammalia a posterior prolongation of the palate, in which an osseous plate is not formed, constitutes the soft palate.

The second change in the Amniota, which also takes place in some Amphibia, is caused by the section of the mesenteron into which the branchial pouches open, becoming, on the atrophy of these structures, converted into the posterior part of the buccal cavity.

The organs derived from the buccal cavity are the tongue, the various salivary glands, and the teeth; but the latter alone will engage our attention here.

The teeth. The teeth are to be regarded as a special product of the oral mucous membrane. It has been shewn by Gegenbaur and Hertwig that in their mode of development they essentially resemble the placoid scales of Elasmobranchii, and that the latter structures extend in Elasmobranchii for a certain distance into the cavity of the mouth.

As pointed out by Gegenbaur, the teeth are therefore to be regarded as more or less specialised placoid scales, whose presence in the mouth is to be explained by the fact that the latter structure is lined by an invagination of the epidermis; The most important developmental point of difference between teeth and placoid scales consists in the fact, that in the case of the former there is a special ingrowth of epiblast to meet a connective tissue papilla which is not found in the latter.

Although the teeth are to be regarded as primitively epiblastic structures, they are nevertheless found in Teleostei and Ganoidei on the hyoid and branchial arches; and very possibly the teeth on some other parts of the mouth are developed in a true hypoblastic region.

The teeth are formed from two distinct organs, viz. an epithelial cap and a connective tissue papilla.

The general mode of development, as has been more especially shewn by the extended researches of Tomes, is practically the same for all Vertebrata, and it will be convenient to describe it as it takes place in Mammalia.

Along the line where the teeth are about to develop, there is formed an epithelial ridge projecting into the subjacent connective tissue, and derived from the innermost columnar layer of the oral epithelium. At the points where a tooth is about to be formed this ridge undergoes special changes. It becomes in the first place somewhat thickened by the development of a number of rounded cells in its interior; so that it becomes constituted of (1) an external layer of columnar cells, and (2) a central core of rounded cells; both of an epithelial nature. In the second place the organ gradually assumes a dome-shaped form (fig. 428, _e_), and covers over a papilla of the subepithelial connective tissue (_p_) which has in the meantime been developed.

[FIG. 428. DIAGRAM SHEWING THE DEVELOPMENT OF THE TEETH. (From Gegenbaur.)

_p._ dental papilla; _e._ enamel organ.]

From the above epithelial structure, which may be called the enamel organ, and from the papilla it covers, which may be spoken of as the dental papilla, the whole tooth is developed. After these parts have become established there is formed round the rudiment of each tooth a special connective tissue capsule; known as the dental capsule.

Before the dental capsule has become definitely formed the enamel organ and the dental papilla undergo important changes. The rounded epithelial cells forming the core of the enamel organ undergo a peculiar transformation into a tissue closely resembling ordinary embryonic connective tissue, while at the same time the epithelium adjoining the dental papilla and covering the inner surface of the enamel organ, acquires a somewhat different structure to the epithelium on the outer side of the organ. Its cells become very markedly columnar, and form a very regular cylindrical epithelium. This layer alone is concerned in forming the enamel. The cells of the outer epithelial layer of the enamel organ become somewhat flattened, and the surface of the layer is raised into a series of short papillæ which project into the highly vascular tissue of the dental sheath. Between the epithelium of the enamel organ and the adjoining connective tissue there is everywhere present a delicate membrane known as the membrana præformativa.

The dental papilla is formed of a highly vascular core and a non-vascular superficial layer adjoining the inner epithelium of the enamel organ. The cells of the superficial layer are arranged so as almost to resemble an epithelium.

The first formation of the hard structures of the tooth commences at the apex of the dental papilla. A calcification of the outermost layer of the papilla sets in, and results in the formation of a thin layer of dentine. Nearly simultaneously a thin layer of enamel is deposited over this, from the inner epithelial layer of the enamel organ (fig. 428). Both enamel and dentine continue to be deposited till the crown of the tooth has reached its final form, and in the course of this process the enamel organ is reduced to a thin layer, and the whole of the outer layer of the dental papilla is transformed into dentine--while the inner portion remains as the pulp.

The root of the tooth is formed later than the crown, but the enamel organ is not prolonged over this part, so that it is only formed of dentine.

By the formation of the root the crown of the tooth becomes pushed outwards, and breaking through its sack projects freely on the surface.

The part of the sack which surrounds the root of the tooth gives rise to the cement, and becomes itself converted into the periosteum of the dental alveolus.

The general development of the enamel organs and dental papillæ is shewn in the diagram (fig. 428). From the epithelial ridge three enamel organs are represented as being developed. Such an arrangement may occur when teeth are successively replaced. The lowest and youngest enamel organ (_e_) has assumed a cap-like form enveloping a dental papilla, but no calcification has yet taken place.

In the next stage a cap of dentine has become formed, while in the still older tooth this has become covered by a layer of enamel. As may be gathered from this diagram, the primitive epithelial ridge from which the enamel organ is formed is not necessarily absorbed on the formation of a tooth, but is capable of giving rise to fresh enamel organs. When the enamel organ has reached a certain stage of development, its connection with the epithelial ridge is ruptured (fig. 428).

The arrangement represented in fig. 428, in which successive enamel organs are formed from the same epithelial ridge, is found in most Vertebrata except the Teleostei. In the Teleostei, however (Tomes), a fresh enamel organ grows inwards from the epithelium for each successively formed tooth.

_The Proctodæum._

In all Vertebrata the cloacal section of the alimentary tract which receives the urinogenital ducts is placed in communication with the exterior by means of an epiblastic invagination, constituting a proctodæum.

This invagination is not usually very deep, and in most instances the boundary wall between it and the hypoblastic cloaca is not perforated till considerably after the perforation of the stomodæum; in Petromyzon, however, its perforation is effected before the mouth and pharynx are placed in communication.

The mode of formation of the proctodæum, which is in general extremely simple, is illustrated by fig. 420 _an_.

In most forms the original boundary between the epiblast of the proctodæum and the hypoblast of the primitive cloaca becomes obliterated after the two have become placed in free communication.

[FIG. 429. DIAGRAMMATIC LONGITUDINAL SECTION THROUGH THE POSTERIOR END OF AN EMBRYO BIRD AT THE TIME OF THE FORMATION OF THE ALLANTOIS.

_ep._ epiblast; _Sp.c._ spinal canal; _ch._ notochord; _n.e._ neurenteric canal; _hy._ hypoblast; _p.a.g._ postanal gut; _pr._ remains of primitive streak folded in on the ventral side; _al._ allantois; _me._ mesoblast; _an._ point where anus will be formed; _p.c._ perivisceral cavity; _am._ amnion; _so._ somatopleure; _sp._ splanchnopleure.]

In Birds the formation of the proctodæum is somewhat more complicated than in other types, owing to the outgrowth from it of the bursa Fabricii.

The proctodæum first appears when the folding off of the tail end of the embryo commences (fig. 429, _an_) and is placed near the front (originally the apparent hind) end of the primitive streak. Its position marks out the front border of the postanal section of the gut.

The bursa Fabricii first appears on the seventh day (in the chick), as a dorsal outgrowth of the proctodæum. The actual perforation of the septum between the proctodæum and the cloacal section of the alimentary tract is not effected till about the fifteenth day of foetal life, and the approximation of the epithelial layers of the two organs, preparatory to their absorption, is partly effected by the tunneling of the mesoblastic tissue between them by numerous spaces.

The hypoblastic section of the cloaca of birds, which receives the openings of the urinogenital ducts, is permanently marked off by a fold from the epiblastic section or true proctodæum, with which the bursa Fabricii communicates.

BIBLIOGRAPHY.

_Alimentary Canal and its appendages._

(561) B. Afanassiew. "Ueber Bau u. Entwicklung d. Thymus d. Säugeth." _Archiv f. mikr. Anat._ Bd. XIV. 1877.

(562) Fr. Boll. _Das Princip d. Wachsthums._ Berlin, 1876.

(563) E. Gasser. "Die Entstehung d. Cloakenöffnung bei Hühnerembryonen." _Archiv f. Anat. u. Physiol., Anat. Abth._ 1880.

(564) A. Götte. _Beiträge zur Entwicklungsgeschichte d. Darmkanals im Hühnchen._ 1867.

(565) W. Müller. "Ueber die Entwickelung der Schilddrüse." _Jenaische Zeitschrift_, Vol. VI. 1871.

(566) W. Müller. "Die Hypobranchialrinne d. Tunicaten." _Jenaische Zeitschrift_, Vol. VII. 1872.

(567) S. L. Schenk. "Die Bauchspeicheldrüse d. Embryo." _Anatomischphysiologische Untersuchungen._ 1872.

(568) E. Selenka. "Beitrag zur Entwicklungsgeschichte d. Luftsäcke d. Huhns." _Zeit. f. wiss. Zool._ 1866.

(569) L. Stieda. _Untersuch. üb. d. Entwick. d. Glandula Thymus, Glandula thyroidea, u. Glandula carotica._ Leipzig, 1881.

(570) C. Fr. Wolff. "De formatione intestinorum." _Nov. Comment. Akad. Petrop._ 1766.

(571) H. Wölfler. _Ueb. d. Entwick. u. d. Bau d. Schilddrüse._ Berlin, 1880.

_Vide_ also Kölliker (298), Götte (296), His (232 and 297), Foster and Balfour (295), Balfour (292), Remak (302), Schenk (303), etc.

_Teeth._

(572) T. H. Huxley. "On the enamel and dentine of teeth." _Quart. J. of Micros. Science_, Vol. III. 1855.

(573) R. Owen. _Odontography._ London, 1840-1845.

(574) Ch. S. Tomes. _Manual of dental anatomy, human and comparative._ London, 1876.

(575) Ch. S. Tomes. "On the development of teeth." _Quart. J. of Micros. Science_, Vol. XVI. 1876.

(576) W. Waldeyer. "Structure and development of teeth." _Stricker's Histology._ 1870.

_Vide_ also Kölliker (298), Gegenbaur (294), Hertwig (306), etc.

INDEX TO VOLUME III.

Abdominal muscles, 675

Abdominal pore, 626, 749

Acipenser, development of, 102; affinities of, 118; comparison of gastrula of, 279; pericardial cavity of, 627

Actinotrocha, 373

Air-bladder of Teleostei, 77; Lepidosteus, 117; blood supply of, 645; general account of, 763; homologies of, 766

Alciope, eye of, 480

Alisphenoid region of skull, 569

Alimentary canal and appendages, development of, 754

Alimentary tract of Ascidia, 18; Molgula, 22; Pyrosoma, 24; Salpa, 31; Elasmobranchii, 52; Teleostei, 75; Petromyzon, 93, 97; Acipenser, 110; Amphibia, 129, 136; Chick, 167; respiratory region of, 754; temporary closure of oesophageal region of, 759

Allantois, development of in Chick, 191, 198; blood-vessels of in Chick, 193; Lacerta, 205, 209; early development of in Rabbit, 229; of Guinea-pig, 264; origin of, 309. _See also_ 'Placenta' and 'Bladder'

Alternation of generations in Ascidians, origin of, 35; in Botryllus, 35; Pyrosoma, 36; Salpa, 36; Doliolum, 36

Alytes, branchial chamber of, 136; yolk-sack of, 139; branchiæ, 141; Müllerian duct of, 710

Amblystoma, ovum of, 120; larva of, 142, 143

Amia, ribs of, 561

Ammocoetes, 95; metamorphosis of, 97; eye of, 498

Amnion, early development of in Chick, 185; later history of in Chick, 196; Lacerta, 204, 210; Rabbit, 229; origin of, 307, 309

Amphibia, development of, 120; viviparous, 121; gastrula of, 277; suctorial mouth of, 317; cerebellum of, 426; infundibulum of, 431; pineal gland of, 433; cerebrum of, 439; olfactory lobes of, 444; nares of, 553; notochord and its sheath, 548; vertebral column of, 554; ribs of, 561; branchial arches of, 574; mandibular and hyoid arches of, 582; columella of, 582; pectoral girdle of, 605; pelvic girdle of, 607; limbs of, 619; heart of, 638; arterial system of, 645; venous system of, 655; excretory system of, 707; vasa efferentia of, 711; liver of, 769; postanal gut of, 774; stomodæum of, 778

Amphiblastula larva of Porifera, 344

Amphioxus, development of, 1; gastrula of, 275; formation of mesoblast of, 292; development of notochord of, 293; head of, 314; spinal nerves of, 461; olfactory organ of, 462; venous system of, 651; transverse abdominal muscle of, 673; generative cells of, 748; liver of, 769; postanal gut of, 772; stomodæum of, 777

Amphistylic skulls, 578

Angular bone, 594

Anterior abdominal vein, 653

Anura, development of, 121; epiblast of, 125; mesoblast of, 128; notochord of, 128; hypoblast of, 129; general growth of embryo of, 131; larva of, 134; vertebral column of, 556; mandibular arch of, 584

Anus of Amphioxus, 7; Ascidia, 18; Pyrosoma, 28; Salpa, 31; Elasmobranchii, 57; Amphibia, 130, 132; Chick, 167; primitive, 324

Appendicularia, development of, 34

Aqueductus vestibuli, 519

Aqueous humour, 497

Arachnida, nervous system of, 409; eye of, 481

Area, embryonic, of Rabbit, 218; epiblast of, 219; origin of embryo from, 228; area opaca of Chick, 150; epiblast, hypoblast, and mesoblast of, 159; area pellucida of Chick, 150; of Lacerta, 202 area vasculosa of Chick, 194; mesoblast of, 160; of Lizard, 209; Rabbit, 228, 229

Arteria centralis retinæ, 503

Arterial system of Petromyzon, 97; constitution of in embryo, 643; of Fishes, 644; of Amphibia, 645; of Amniota, 647

Arthropoda, head of, 313; nervous system of, 409; eye of, 480; excretory organs of, 688

Articular bone of Teleostei, 581; of Sauropsida, 588

Ascidia, development of, 9

Ascidians. _See_ 'Tunicata'

Ascidiozooids, 25

Atrial cavity of Amphioxus, 7; Ascidia, 18; Pyrosoma, 24

Atrial pore of Amphioxus, 7; Ascidia, 20; Pyrosoma, 28; Salpa, 32

Auditory capsules, ossifications in, 595, 596

Auditory involution of Elasmobranchii, 57; Teleostei, 73; Petromyzon, 89, 92; Acipenser, 106; Lepidosteus, 114; Amphibia, 127; Chick, 170

Auditory nerve, development of, 459

Auditory organs, of Ascidia, 15; of Salpa, 31; of Ammocoetes, 98; Ganoidei, 108, 114; of Amphibia, 127; of Aves, 170; general development of, 512; of aquatic forms, 512; of land forms, 513; of Coelenterata, 513; of Mollusca, 515; of Crustacea, 516; of Vertebrata, 517; of Cyclostomata, 89, 92, 518; of Teleostei, Lepidosteus and Amphibia, 518; of Mammalia, 519; accessory structures of, 527; of Tunicata, 528

Auriculo-ventricular valves, 642

Autostylic skulls, 579

Aves, development of, 145; cerebellum of, 426; mid-brain of, 427; infundibulum of, 431; pineal gland of, 434; pituitary body of, 436; cerebrum of, 439; olfactory lobes of, 444; spinal nerves of, 449; cranial nerves of, 455; vagus of, 458; glossopharyngeal of, 458; vertebral column of, 557; ossification of vertebral column of, 558; branchial arches of, 572, 573; pectoral girdle of, 603; pelvic girdle of, 608; heart of, 637; arterial system of, 647; venous system of, 658; muscle-plates of, 670; excretory organs of, 714; mesonephros of, 715; pronephros of, 718; Müllerian duct of, 718, 720; nature of pronephros of, 721; connection of Müllerian duct with Wolffian in, 720; kidney of, 722; lungs of, 764; liver of, 769; postanal gut of, 774

Axolotl, 142, 143; ovum of, 120; mid-brain of, 427; mandibular arch of, 583

Basilar membrane, 524

Basilar plate, 565

Basipterygium, 612

Basisphenoid region of skull, 569

Bilateral symmetry, origin of, 373-376

Bile duct, 770

Bladder, Amphibia, 131; of Amniota, 726

Blastodermic vesicle, of Rabbit, first development of, 217; of 7th day, 222; Guinea-pig, 263; meaning of, 291

Blastoderm of Pyrosoma, 24; Elasmobranchii, 41; Chick, 150; Lacerta 202

Blastopore, of Amphioxus, 2; of Ascidia, 11; Elasmobranchii, 42, 54, 62; Petromyzon, 87; Acipenser, 104; Amphibia, 125, 130; Chick, 153; Rabbit, 216; true Mammalian, 226; comparative history of closure of, 284, 288; summary of fate of, 340; relation of to primitive anus, 324

Blood-vessels, development of, 633

Body cavity, of Ascidia, 21; Molgula, 21; Salpa, 31; Elasmobranchii, 47; of Teleostei, 75; Petromyzon, 94; Chick, 169; development of in Chordata, 325; views on origin of, 356-360, 377; of Invertebrata, 623; of Chordata, 624; of head, 676

Bombinator, branchial chamber of, 136; vertebral column of, 556

Bonellia, excretory organs of, 687

Bones, origin of cartilage bones, 542; origin of membrane bones, 543; development of, 543; homologies of membrane bones, 542; homologies of cartilage bones, 545

Brachiopoda, excretory organs of, 683; generative ducts of, 749

Brain, of Ascidia, 11, 15; Elasmobranchii, 56, 59, 60; Teleostei, 77; Petromyzon, 89, 92; Acipenser, 105; Lepidosteus, 113; early development of in Chick, 170; flexure of in Chick, 175; later development of in Chick, 176; Rabbit, 229; general account of development of, 419; flexure of, 420; histogeny of, 422

Branchial arches, præoral, 570; disappearance of posterior, 573; dental plates of in Teleostei, 574; relation of to head cavities, 571; _see_ 'Visceral arches'

Branchial chamber of Amphibia, 136

Branchial clefts, of Amphioxus, 7; of Ascidia, 18, 20; Molgula, 23; Salpa, 32; of Elasmobranchii, 57, 59-61; Teleostei, 77; Petromyzon, 91, 96; Acipenser, 105; Lepidosteus, 114, 116; Amphibia, 132, 133; Chick, 178; Rabbit, 231; præoral, 312, 318; of Invertebrata, 326; origin of, 326

Branchial rays, 574

Branchial skeleton, development of, 572, 592; of Petromyzon, 96, 312, 571; of Ichthyopsida, 572; dental plates of in Teleostei, 574; relation of to head cavities, 572

Branchiæ, external of Elasmobranchii, 61, 62; of Teleostei, 77; Acipenser, 107; Amphibia, 127, 133, 135

Brood-pouch, of Salpa, 29; Teleostei, 68; Amphibia, 121

Brown tubes of Gephyrea, 686

Bulbus arteriosus, of Fishes, 638; Amphibia, 639

Bursa Fabricii, 167, 779

Canalis auricularis, 639

Canalis reuniens, 521

Capitellidæ, excretory organs of, 683

Carcharias, placenta of, 66

Cardinal vein, 652

Carnivora, placenta of, 250

Carpus, development of, 620

Cartilage bones of skull, 595; homologies of, 595

Cat, placenta of, 250

Caudal swellings of Elasmobranchii, 46, 55; Teleostei, 72; Chick, 162, 170

Cephalic plate of Elasmobranchii, 55

Cephalochorda, development of, 1

Cephalopoda, eyes of, 473-477

Cerebellum, Petromyzon, 93; Chick, 176; general account of development of, 424, 425

Cerebrum of Petromyzon, 93, 97; Chick, 175; general development of, 429, 438; transverse fissure of, 443

Cestoda, excretory organs of, 681

Cetacea, placenta, 255

Chætognatha, nervous system of, 349; eye of, 479; generative organs of, 743; generative ducts of, 749

Chætopoda, head of, 313; eyes of, 479; excretory organs of, 683; generative organs of, 743; generative ducts of, 749

Charybdæa, eye of, 472

Cheiroptera, placenta of, 244

Cheiropterygium, 618; relation of to ichthyopterygium, 621

Chelonia, development of, 210; pectoral girdle of, 603; arterial system of, 649

Chick, development of, 145; general growth of embryo of, 170; rotation of embryo of, 173; foetal membranes of, 185; epiblast of, 150, 166; optic nerve and choroid fissure of, 500

Chilognatha, eye of, 481

Chilopoda, eye of, 481

Chimæra, lateral line of, 539; vertebral column of, 548; nares of, 533

Chiromantis, oviposition of, 121

Chorda tympani, development of, 460

Chordata, ancestor of, 311; branchial system of, 312; evidence from Ammocoetes, 312; head of, 312; mouth of, 318; table of phylogeny of, 327

Chorion, 237; villi of, 237, 257

Choroid coat, Ammocoetes, 99; general account of, 487

Choroid fissure, of Vertebrate eye, 486, 493; of Ammocoetes, 498; comparative development of, 500; of Chick, 501; of Lizards, 501; of Elasmobranchii, 502; of Teleostei, 503; Amphibia, 503; Mammals, 503, 504

Choroid gland, 320

Choroid pigment, 489

Choroid plexus, of fourth ventricle, 425; of third ventricle, 432; of lateral ventricle, 442

Ciliated sack of Ascidia, 18; Pyrosoma, 26; Salpa, 31

Ciliary ganglion, 461

Ciliary muscle, 490

Ciliary processes, 488; comparative development of, 506

Clavicle, 600

Clitoris, development of, 727

Clinoid ridge, 569

Cloaca, 766

Coccygeo-mesenteric vein, 661

Cochlear canal, 519

Coecilia, development of, 143; pronephros of, 707; mesonephros of, 709; Müllerian duct of, 710

Coelenterata, larvæ of, 367; eyes of, 471; auditory organs of, 513; generative organs of, 741

Columella auris, 529; of Amphibia, 582; of Sauropsida, 588

Commissures, of spinal cord, 417; of brain, 431, 432, 439, 443

Coni vasculosi, 724

Conus arteriosus, of Fishes, 638; of Amphibia, 638

Coracoid bone, 599

Cornea, of Ammocoetes, 99; general development of, 495; corpuscles of, 496; comparative development of, 499; of Mammals, 499

Coronoid bone, 595

Corpora geniculata interna, 428

Corpora quadrigemina, 428

Corpora striata, development of, 437

Corpus callosum, development of, 443

Corti, organ of, 522; structure of, 525; fibres of, 525; development of, 526

Cranial flexure, of Elasmobranchii, 58, 60; of Teleostei, 77; Petromyzon, 93, 94; of Amphibia, 131, 132; Chick, 174; Rabbit, 231; characters of, 321; significance of, 322

Cranial nerves, development of, 455; relation of to head cavities, 461; anterior roots of, 462-464; view on position of roots of, 466

Crocodilia, arterial system of, 649

Crura cerebri, 429

Crustacea, nervous system of, 411; eye of, 481; auditory organs of, 515; generative cells of, 745; generative ducts of, 751

Cupola, 524

Cutaneous muscles, 676

Cyathozooid, 25

Cyclostomata, auditory organs of, 517; olfactory organ of, 532; notochord and vertebral column of, 546, 549; abdominal pores of, 626; segmental duct of, 700; pronephros of, 700; mesonephros of, 700; generative ducts of, 733, 749; venous system of, 651; excretory organs of, 700

Cystignathus, oviposition of, 122

Dactylethra, branchial chamber of, 136; branchiæ of, 136; tadpole of, 140

Decidua reflexa, of Rat, 242; of Insectivora, 243; of Man, 245

Deiter's cells, 526

Dental papilla, 777

Dental capsule, 777

Dentary bone, 595

Dentine, 780

Descemet's membrane, 496

Diaphragm, 631; muscle of, 676

Dipnoi, nares of, 534; vertebral column of, 548; membrane bones of skull of, 592; heart of, 638; arterial system of, 645; excretory system of, 707; stomodæum of, 777

Diptera, eye of, 481

Discophora, excretory organs of, 687

Dog, placenta of, 248

Dohrn, on relations of Cyclostomata, 84; on ancestor of Chordata, 311, 319

Doliolum, development of, 28

Ductus arteriosus, 649

Ductus Botalli, 648

Ductus Cuvieri, 654

Ductus venosus Arantii, 663

Dugong, heart of, 642

Dysticus, eye of, 481

Ear, _see_ 'Auditory organ'

Echinodermata, secondary symmetry of larva of, 380; excretory organs of, 689; generative ducts of, 752

Echinorhinus, lateral line of, 539; vertebral column of, 548

Echiurus, excretory organs of, 686

Ectostosis, 543

Edentata, placenta of, 248, 250, 256

Eel, generative ducts of, 703

Egg-shell of Elasmobranchii, 40; Chick, 146

Elasmobranchii, development of, 40; viviparous, 40; general features of development of, 55; gastrula of, 281; development of mesoblast of, 294; notochord of, 294; meaning of formation of mesoblast of, 295; restiform tracts of, 425; optic lobes of, 427; cerebellum of, 425; pineal gland of, 432; pituitary body of, 435; cerebrum of, 438; olfactory lobes of, 444; spinal nerves, 449; cranial nerves of, 457; sympathetic nervous system of, 466; nares of, 533; lateral line of, 539; vertebral column of, 549; ribs of, 560; parachordals of, 567; mandibular and hyoid arches of, 576; pectoral girdle of, 600; pelvic girdle of, 607; limbs of, 609; pericardial cavity of, 627; arterial system of, 644; venous system of, 651; muscle-plates of, 668; excretory organs of, 690; constitution of excretory organs in adult of, 697; spermatozoa of, 747; swimming-bladder of, 763; intestines of, 767; liver of, 769; postanal gut of, 772

Elæoblast of Pyrosoma, 28; Salpa, 30

Elephant, placenta of, 249

Embolic formation of gastrula, 333

Enamel organ, 777

Endolymph of ear, 522

Endostosis, 543

Endostyle of Ascidia, 18, 759; Pyrosoma, 25; Salpa, 32

Epiblast, of Elasmobranchii, 47; Teleostei, 71, 75; Petromyzon, 86; Lepidosteus, 112; Amphibia, 122, 125; Chick, 149, 166; Lacerta, 203; Rabbit, 216, 219; origin of in Rabbit, 221; comparative account of development of, 300

Epibolic formation of gastrula, 334

Epichordal formation of vertebral column, 556

Epicrium glutinosum, 143

Epidermis, in Coelenterata, 393; protective structures of, 394

Epididymis, 724

Epigastric vein, 653

Episkeletal muscles, 676

Episternum, 602

Epoophoron, 725

Ethmoid bone, 597

Ethmoid region of skull, 570

ethmo-palatine ligament of Elasmobranchs, 576

Euphausia, eye of, 483

Eustachian tube, of Amphibia, 135; Chick, 180; Rabbit, 232; general development of, 528

Excretory organs, general constitution of, 680; of Platyelminthes, 680; of Mollusca, 681; of Polyzoa, 682; of Brachiopoda, 683; of Chætopoda, 683; of Gephyrea, 686; of Discophora, 687; of Arthropoda, 688; of Nematoda, 689; of Echinodermata, 689; constitution of in Craniata, 689; of Elasmobranchii, 690; constitution of in adult Elasmobranch, 697; of Petromyzon, 700; of Myxine, 701; of Teleostei,701; of Ganoidei, 704; of Dipnoi, 707; of Amphibia, 707; of Amniota, 713; comparison of Vertebrate and Invertebrate, 737

Excretory system, of Elasmobranchii, 49; Teleostei, 78; Petromyzon, 95, 98; Acipenser, 99; Amphibia, 133

Exoccipital bone, 595

Exoskeleton, dermal, 393-395; epidermal, 393-396

External generative organs, 726

Extra-branchial skeleton, 572

Eye, of Ascidia, 16; Salpa, 31; Elasmobranchii, 56, 57, 58; Teleostei, 73; Petromyzon, 92, 98; Aves, 170; Rabbit, 229; general development of, 470; evolution of, 470, 471; simple, 480; compound, 481; aconous, 482; pseudoconous, 482; of Invertebrata, 471; of Vertebrata, 483; comparative development of Vertebrate, 497; of Ammocoetes, 497; of Tunicata, 507; of Chordata, general views on, 508; accessory eyes of Fishes, 509; muscles of, 677

Eyelids, development of, 506

Falciform ligament, 757

Falx cerebri, 439

Fasciculi teretes, of Elasmobranchii, 426

Feathers, development of, 396

Fenestra rotunda and ovalis, 529

Fertilization, of Amphioxus, 2; of Urochorda, 9; Salpa, 29; Elasmobranchii, 46; of Teleostei, 68; Petromyzon, 84; Amphibia, 120; Chick, 145; Reptilia, 202; meaning of, 331

Fifth nerve, development of, 460

Fifth ventricle, 443

Fins, of Elasmobranchii, 62; Teleostei, 78; Petromyzon, 94, 95; Acipenser, 109; Lepidosteus, 118; relation of paired to unpaired, 611, 612; development of pelvic, 614; development of pectoral, 615; views on nature of paired fins, 616

Fissures of spinal cord, 417

Foetal development, 360; secondary variations in, 361

Foot, 618

Foramen of Munro, 430, 438

Foramen ovale, 642

Fore-brain, of Elasmobranchii, 55, 59, 60; Petromyzon, 93; general development of, 428

Formative cells, of Chick, 154

Fornix, development of, 443

Fornix of Gottsche, 428

Fourth nerve, 464

Frontals, 592

Frontonasal process of Chick, 179

Gaertner's canals, 724

Gall-bladder, 770

Ganoidei, development of, 102; relations of, 118; nares of, 534; notochord of, 546; vertebral column of, 546, 553; ribs of, 561; pelvic girdle of, 606; arterial$ system of, 645; excretory organs of, 704; generative ducts of, 734

Gastropoda, eye of, 472

Gastrula, of Amphioxus, 2; of Ascidia, 10; Elasmobranchii, 43, 44; Petromyzon, 86; Acipenser, 103; Amphibia, 123; comparative development of, in Invertebrata, 275; comparison of Mammalian, 291; phylogenetic meaning of, 333; ontogeny of (general), 333; phylogeny of, 338-343; secondary types of, 341

Geckos, vertebral column of, 557

Generative cells, development of, 741; origin of in Coelenterata, 741; of Invertebrata, 743; of Vertebrata, 746

Generative ducts, of Teleostei, 704, 735; of Ganoids, 704; of Cyclostomata, 733; origin of, 733; of Lepidosteus, 735, 750; development and evolution of, 748; of Coelenterata, 748; of Sagitta, 749; of Tunicata, 749; Chætopoda, Gephyrea, etc., 749; of Mollusca, 751; of Discophora, 751; of Echinodermata, 752

Generative system of Elasmobranchii, 51

Gephyrea, nervous system of, 412; excretory organs of, 686; generative cells of, 743; generative ducts of, 749

Germinal disc, of Elasmobranchii, 40; Teleostei, 68; Chick, 147

Germinal epithelium, 746

Germinal layers, summary of organs derived from, in Vertebrata, 304; historical account of views of, 332; homologies of in the Metazoa, 345

Germinal wall of Chick, 152, 159; structure and changes of, 160

Geryonia, auditory organ of, 515

Gill of Salpa, 31

Giraldes, organ of, 725

Glands, epidermic, development of, 397

Glomerulus, external, of Chick, 716

Glossopharyngeal nerve, development of, 456, 457

Grey matter of spinal cord, 417; of brain, 423

Growth in length of Vertebrate embryo, 306

Guinea-pig, primitive streak of, 223; notochord of, 226; placenta of, 242; development of, 262

Gymnophiona, _see_ 'Coecilia'

Habenula perforata, 525

Hairs, development of, 396

Halichærus, placenta of, 250

Hand, 619

Head, comparative account of, 313; segmentation of, 314

Head cavities, of Elasmobranchii, 50; Petromyzon, 90, 96; Amphibia, 127; general development of, 676

Head-fold of Chick, 157, 167

Head kidney, _see_ 'Pronephros'

Heart, of Pyrosoma, 25; Elasmobranchii, 50, 58; Petromyzon, 94, 97; Acipenser, 106; Chick, 170; first appearance of in Rabbit, 230; general development of, 633; of Fishes, 635, 637; of Mammalia, 638; of Birds, 637, 639; meaning of development of, 637; of Amphibia, 638; of Amniota, 639; change of position of, 643

Hind-brain, Elasmobranchii, 55, 59, 60; Petromyzon, 93; general account of, 424

Hippocampus major, development of, 442

Hirudo, development of blood-vessels of, 633; excretory organs of, 688

Horse, placenta of, 253

Hyaloid membrane, 492

Hylodes, oviposition of, 121; metamorphosis of, 137

Hyobranchial cleft, 572

Hyoid arch, of Chick, 179; general account of, 572, 575; modifications of, 573, 577; of Elasmobranchii, 576; of Teleostei, 577; of Amphibia, 582; of Sauropsida, 588; of Mammalia, 589

Hyomandibular bar of Elasmobranchii, 576, 577; of Teleostei, 579; of Amphibia, 582

Hyomandibular cleft, of Petromyzon, 91; Chick, 179; general account of, 572

Hyostylic skulls, 582

Hypoblast of Elasmobranchii, 51; Teleostei, 71, 75; Petromyzon, 86; Acipenser, 104; Lepidosteus, 113; Amphibia, 122, 129; Chick, 151, 167; Lacerta, 203; Rabbit, 215, 216, 219; origin of in Rabbit, 220

Hyposkeletal muscles, 675

Hyrax, placenta of, 249

Incus, 529, 590

Infraclavicle, 600

Infundibulum of Petromyzon, 92; Chick, 175; general development of, 430

Insectivora, placenta of, 243

Insects, nervous system of, 410; eye of, 481; generative organs of, 745; generative ducts of, 751

Intercalated pieces of vertebral column, 551

Interclavicle, homologies of, 602

Intermediate cell-mass of Chick, 183

Intermuscular septa, 672

Interorbital septum, 570

Interrenal bodies, 665

Iris, 489; comparative development of, 506

Iris of Ammocoetes, 98

Island of Reil, 444

Jacobson's organ, 537

Jugal bone, 594

Kidney, _see_ 'Metanephros'

Labia majora, development of, 727

Labial cartilages, 597

Labium tympanicum, 525; vestibulare, 525

Lacertilia, general development of, 202; nares of, 537; pectoral girdle of, 603; pelvic girdle of, 607; arterial system of, 649

Lacrymal bone, 593

Lacrymal duct, 506

Lacrymal glands, 506

Læmargus, vertebral column of, 548

Lagena, 524

Lamina spiralis, 524

Lamina terminalis, 438

Larva of Amphioxus, 2; of Ascidia, 15-21; Teleostei, 81; Petromyzon, 89, 95; Lepidosteus, 117, 318; Amphibia, 134, 142; types of, in the Invertebrata, 363

Larvæ, nature, origin, and affinities of, 360-386; secondary variations of less likely to be retained, 362; ancestral history more fully recorded in, 362; secondary variations in development of, 363; ontogenetic record of secondary variations in, 361; of freshwater and land animals, 362; types of, 362; phosphorescence of, 364; of Coelenterata, 367; table of, 365; of Invertebrata, 367 et seq.

Larynx, 766

Lateral line sense organs, 538; comparison of, with invertebrate, 538; development of, in Teleostei, 538; development of, in Elasmobranchii, 539

Lateral ventricle, 438; anterior cornu of, 440; descending cornu of, 440; choroid plexus of, 443

Layers, formation of, in Elasmobranchii, 41, 56; Teleostei, 71; Petromyzon, 85; Acipenser, 103; Lepidosteus, 111; Amphibia, 121; Chick, 150, 152; Lacerta, 202; Rabbit, 215-227; comparison of Mammalia with lower forms, 226, 289; comparison of formation of in Vertebrata, 275; origin and homologies of, in the Metazoa, 331

Leech, _see_ 'Hirudo'

Lemuridæ, placenta, 256

Lens, of Elasmobranchii, 57, 58; Petromyzon, 94, 99; Acipenser, 106; Lepidosteus, 115; Amphibia, 127; Chick, 177; of Vertebrate eyes, 485; general account of, 493; capsule of, 493; comparative development of, 499; of Amphibia, Teleostei, Lepidosteus, 499

Lepidosteus, development of, 111; larva of, 117; relations of, 119; spinal nerves of, 455; ribs of, 561; generative ducts of, 704, 735; swimming-bladder of, 763

Ligamentum pectinatum, 490

Ligamentum suspensorium, 557, 558

Ligamentum vesicæ medium, 239

Limbs, of Elasmobranchii, 59; Teleostei, 80; first appearance of in Chick, 184; Rabbit, 232; muscles of, 673; of Fishes, 609; relation of, to unpaired fins of Fishes, 611, 612; of Amphibia, 618

Liver of Teleostei, 78; Petromyzon, 95, 96; Acipenser, 110; Amphibia, 130; general account of, 769

Lizard, development of, 202; general growth of embryo of, 208; Müllerian duct of, 721

Lizzia, eye of, 471

Lobi inferiores, 431

Lungs of Amphibia, 137; development of, 763; homology of, 766

Lymphatic system, 664

Malleus, 529, 591; views on, 591

Malpighian bodies, development of accessory in Elasmobranchs, 695

Mammalia, development of, 214; comparison of gastrula of, 291; cerebellum of, 427; infundibulum of, 431; pineal gland of, 434; pituitary body of, 436; cerebrum of, 439; spinal nerves of, 449; sympathetic of, 466; vertebral column of, 558; branchial arches of, 573, 574; mandibular and hyoid arches of, 589; pectoral girdle of, 604; pelvic girdle of, 608; heart of, 636; arterial system of, 647; venous system of, 661; muscle-plates of, 671; mesonephros of, 714; testicular network of, 724; urinogenital sinus of, 727; spermatozoa of, 747; lungs of, 765; intestines of, 768; liver of, 769; postanal gut of, 774; stomodæum of, 775

Mammary gland, development of, 398

Man, placenta of, 244; general account of development of, 265; characters of embryo of, 270

Mandibular arch of Elasmobranchii, 62, 576; Petromyzon, 91; Acipenser, 106, 116; Chick, 179; general account of, 572, 575; modification of to form jaws, 573, 575; of Teleostei, 580; of Amphibia, 582; Sauropsida, 588; Mammalia, 589

Mandibular bar, evolution of, 311, 321

Manis, placenta of, 256

Marsupial bones, 608

Marsupialia, foetal membranes of, 240; cerebellum of, 426; corpus callosum of, 443; uterus of, 726

Maxilla, 594

Meatus auditorius externus, of Chick, 181; development of, 527

Meckelian cartilage, of Elasmobranchii, 576; of Teleostei, 581; of Amphibia, 584, 585; of Sauropsida, 588; of Mammalia, 590

Mediastinum anterior and posterior, 630

Medulla oblongata, of Chick, 176; general development of, 425

Medullary plate of Amphioxus, 4, 5; of Ascidia, 11; Elasmobranchii, 44, 47, 55; Teleostei, 72; Petromyzon, 88; Acipenser, 104; Lepidosteus, 111; Amphibia, 126, 127, 131; Chick, 159; Lacerta, 204; Rabbit, 223, 227, 228; primitive bilobed character of, 303, 317

Medusæ, auditory organs of, 513

Membrana capsulo-pupillaris, 494, 504, 507

Membrana elastica externa, 546

Membrana limitans of retina, 491

Membrana tectoria, 522, 525

Membrane bones, of Amphibia, 582; of Sauropsida, 588; of Mammalia, 590; of mandibular arch, 593; of pectoral girdle, 599, 602; origin of, 592; homologies of, 593

Membranous labyrinth, development of in Man, 519

Menobranchus, branchial arches of, 142

Mesenteron of Elasmobranchii, 43; Teleostei, 75; Petromyzon, 85; Acipenser, 104; Amphibia, 123, 124, 129; Chick, 167; general account of, 754

Mesentery, 626, 756

Mesoblast, of Amphioxus, 6; Ascidia, 17, 20; Pyrosoma, 24; Salpa, 30; Elasmobranchii, 44, 47; Teleostei, 75; Petromyzon, 86; Acipenser, 105; Lepidosteus, 113; Amphibia, 125, 128, 129; of Chick, 154, 167; double origin of in Chick, 154, 158, 159; origin of from lips of blastopore in Chick, 158; of area vasculosa of Chick, 160; Lacerta, 203; origin of in Rabbit, 218, 223; of area vasculosa in Rabbit, 227; comparative account of formation of, 292; discussion of development of in Vertebrata, 297; meaning of development of in Amniota, 298; phylogenetic origin of, 346; summary of ontogeny of, 349-352; views on ontogeny of, 352-360

Mesoblastic somites, of Amphioxus, 6; Elasmobranchii, 48, 55; Petromyzon, 88; Acipenser, 105; Lepidosteus, 114; Amphibia, 129, 131; Chick, 161, 180; Rabbit, 228; development of in Chordata, 325; meaning of development of, 331; of head, 676

Mesogastrium, 758

Mesonephros, of Teleostei, 78, 702; Petromyzon, 95, 98, 700; Acipenser, 110, 705; Amphibia, 134, 708; Chick, 184, 714; general account of, 690; development of in Elasmobranchs 691; of Cyclostomata, 700; Ganoidei, 705; sexual and non-sexual part of in Amphibia, 710; of Amniota, 713, 724; summary and general conclusions as to, 729; relation of to pronephros, 731

Mesopterygium, 616

Metagenesis of Ascidians, 34

Metamorphosis of Amphibia, 137, 140

Metanephros, 690; development of in Elasmobranchii, 697; of Amphibia, 712; of Amniota, 713; of Chick, 722; of Lacertilia, 723; phylogeny of, 736

Metapterygium, 616

Metapterygoid, of Elasmobranchii, 576; of Teleostei, 581

Metazoa, evolution of, 339, 342; ancestral form of, 333, 345

Mid-brain, of Elasmobranchii, 55, 58, 59; Petromyzon, 92; general account of development of, 427

Moina, generative organs of, 745

Molgula, development of, 22

Mollusca, nervous system of, 414; eyes of, 472; auditory organs of, 515; excretory organs of, 681

Monotremata, foetal membranes of, 240; cerebellum of, 426; corpus callosum of, 443; cerebrum of, 443; urinogenital sinus of, 726

Mormyrus, generative ducts of, 704

Mouth, of Amphioxus, 7; of Ascidia, 18; Pyrosoma, 27; Salpa, 31; Elasmobranchii, 57, 60, 61, 62; Petromyzon, 92, 94, 95, 99; Acipenser, 107; Lepidosteus, 118; Amphibia, 129, 132, 134; Rabbit, 231; origin of, 317

Mouth, suctorial, of Petromyzon, 99; Acipenser, 107; Lepidosteus, 116, 317; Amphibia, 133, 141, 317

Müllerian duct, 690; of Elasmobranchs, 693; of Ganoids, 704; of Amphibia, 710; of Aves, 717, 720; opening of into cloaca, 727; origin of, 733; summary of development of, 733; relation of to pronephros, 733

Muscle-plates, of Amphioxus, 6; Elasmobranchii, 49, 668; Teleostei, 670; Petromyzon, 94; Chick, 183, 670; general development of, 669; of Amphibia, 670; Aves, 670; of Mammalia, 671; origin of muscles from, 672

Muscles, of Ascidia, 11, 17; development of from muscle-plates, 672; of limbs, 673; of head, 676; of branchial arches, 678; of eye, 678

Muscular fibres, epithelial origin of, 667

Muscular system, development of, 667; of Chordata, 668

Mustelus, placenta of, 66

Myoepithelial cells, 667

Mysis, auditory organ of, 517

Myxine, ovum of, 100; olfactory organ of, 533; portal sinus of, 652; excretory system of, 701

Nails, development of, 397

Nares, of Acipenser, 108; of Ichthyopsida, 534; development of in Chick, 535; development of in Lacertilia, 537; development of in Amphibia, 537

Nasal bones, 592

Nasal pits, Acipenser, 108; Chick, 176; general development of, 531

Nematoda, excretory organs of, 689; generative organs of, 745; generative ducts of, 752

Nemertines, nervous system of, 311; excretory organs of, 681

Nerve cord, origin of ventral, 378

Nerves, spinal, 449; cranial, 455-466

Nervous system, central, general account of development of in Vertebrata, 415; conclusions as to, 445; sympathetic, 466

Nervous system, of Amphioxus, 4; Ascidia, 15, 16; Molgula, 22; Pyrosoma, 24, 25; Salpa, 30, 31; Elasmobranchii, 44; Teleostei, 77; Petromyzon, 89, 93; Acipenser, 105; Amphibia, 126; comparative account of formation of central, 301; of Sagitta, 349; origin of in Coelenterata, 349; of præoral lobe, 377, 380; evolution of, 400-405; development of in Invertebrates, 406; of Arthropoda, 408; of Gephyrea, 412; Mollusca, 414

Neural canal, of Ascidia, 10; Teleostei, 72; Petromyzon, 88; Acipenser, 105; Lepidosteus, 114; Amphibia, 126, 131; Chick, 166, 171; Lacerta, 208; closure of in Frog and Amphioxus, 279; closure of in Elasmobranchii, 284; phylogenetic origin of, 316

Neural crest, 449, 456, 457

Neurenteric canal, of Amphioxus, 4, 5; Ascidia, 10; Elasmobranchii, 54; Petromyzon, 88; Acipenser, 105; Lepidosteus, 113; Aves, 162; Lacerta, 203, 206; general account of, 323; meaning of, 323

Newt, ovum of, 120; development of, 125; general growth of, 141

Notidanus, vertebral column of, 548; branchial arches of, 572

Notochord of Amphioxus, 6; Ascidia, 11, 17; Elasmobranchii, 51; Teleostei, 74; Petromyzon 86, 94; Acipenser, 104; Lepidosteus, 113; Amphibia, 128, 129; Chick, 157; canal of, in Chick, 163; Lacerta, 204, 205; Guinea-pig, 226; comparative account of formation of, 292, 325; sheath of, 545; later histological changes in, 546; cartilaginous sheath of, 547; in head, 566; absence of in region of trabeculæ, 567

Notodelphys, brood-pouch of, 121; branchiæ of, 140

Nototrema, brood-pouch of, 121

Nucleus pulposus, 559

Oceania, eye of, 471

Occipital bone, 595

OEsophagus, solid, of Elasmobranchii, 61, 759; of Teleostei, 78

Olfactory capsules, 571

Olfactory lobes, development of, 444

Olfactory nerves, Ammocoetes, 99; general development of, 464

Olfactory organ, of aquatic forms, 531; Insects and Crustacea, 531; of Tunicata, 532; of Amphioxus, 532; of Vertebrata, 533; Petromyzon, 533; of Myxine, 533

Olfactory sacks, of Elasmobranchii, 60; Teleostei, 73; Petromyzon, 92, 97; Acipenser, 106, 108; Lepidosteus, 116; Chick, 176

Oligochæta, excretory organs of, 683

Olivary bodies, 426

Omentum, lesser and greater, 757

Onchidium, eye of, 478

Opercular bones, 593

Operculum, of Teleostei, 77; Acipenser, 107; Lepidosteus, 117, 118; Amphibia, 135

Ophidia, development of, 210; arterial system of, 649; venous system of, 656

Optic chiasma, 430, 493

Optic cup, retinal part of, 488; ciliary portion of, 489

Optic lobes, 428

Optic nerve, development of, 492; comparative development of, 500

Optic thalami, development of, 431

Optic vesicle, of Elasmobranchii, 57-59; Teleostei, 74, 499; Petromyzon, 89, 92; Acipenser, 106; Lepidosteus, 115; Chick, 170; Rabbit, 229; general development of, 429; formation of secondary, 487; obliteration of cavity of, 488; comparative development of, 499; of Lepidosteus and Teleostei, 499. _See also_ 'Eye'

Ora serrata, 488

Orbitosphenoid region of skull, 570

Organs, classification of, 391; derivation of from germinal layers, 392

Orycteropus, placenta of, 249

Otic process of Axolotl, 583; of Frog, 585 et seq.

Otoliths, 512

Oviposition, of Amphioxus, 1; Elasmobranchii, 40; Teleostei, 68; Petromyzon, 84; Amphibia, 121; Reptilia, 202

Ovum, of Amphioxus, 1; Pyrosoma, 23; Elasmobranchii, 40; Teleostei, 68; Petromyzon, 83; Myxine, 100; Acipenser, 102; Lepidosteus, 111; Amphibia, 120; Chick, 146; Reptilia, 202; Mammalia, 214; of Porifera, 741; migration of in Coelenterata, 742; Vertebrata, 746

Palatine bone, of Teleostei, 580; origin of, 594

Pancreas, Acipenser, 110; general development of, 770

Pancreatic cæca, of Teleostei, etc. 768

Papillæ, oral, of Acipenser, 108; Lepidosteus, 116

Parachordals, 565, 566

Parasphenoid bone, 594

Parepididymis, 725

Parietal bones, 592

Paroophoron, 725

Parovarium, 725

Pectoral girdle, 599; of Elasmobranchs, 600; of Teleostei, 600; of Amphibia and Amniota, 601; comparison of with pelvic, 608

Pecten, eye of, 479

Pecten, of Ammocoetes, 498; of Chick, 501; Lizard, 501; Elasmobranchs, 501

Pedicle, of Axolotl, 484; of Frog, 485

Pelobates, branchial apertures of, 136; vertebral column of, 556

Pelodytes, branchial chamber of, 135

Pelvic girdle, 606; of Fishes, 606; Amphibia and Amniota, 607; of Lacertilia, 607; of Mammalia, 608; comparison with pectoral, 608

Penis, development of, 727

Peribranchial cavity, of Amphioxus, 7; of Ascidia, 18; Pyrosoma, 24

Pericardial cavity, of Pyrosoma, 26; Elasmobranchii, 49; Petromyzon, 94; general account of, 626; of Fishes, 627; of Amphibia, Sauropsida and Mammalia, 628

Perichordal formation of vertebral column, 556

Perilymph of ear, 523

Periotic capsules, ossifications in, 595, 596

Peripatus, nervous system of, 409; eye of 480; excretory organs of, 688

Peritoneal membrane, 626

Petromyzon, development of, 83; affinities of, 83, 84; general development of, 87; hatching of, 89; comparison of gastrula of, 280; branchial skeleton of, 312, 572; cerebellum of, 425; pineal gland of, 434; pituitary body of, 436; cerebrum of, 439; auditory organ of, 517; olfactory organ of, 533; comparison of oral skeleton of with Tadpole, 586; pericardial cavity of, 627; abdominal pores of, 626; venous system of, 651; excretory organs of, 700; segmental duct of, 700; pronephros of, 700; mesonephros of, 700; thyroid body of, 760; postanal gut of, 774; stomodæum of, 775

Phosphorescence of larvæ, 364

Phylogeny, of the Chordata, 327; of the Metazoa, 384

Pig, placenta of, 251; mandibular and hyoid arches of, 589

Pineal gland, of Petromyzon, 93; Chick, 175; general development of, 432; nature of, 432, 434

Pipa, brood-pouch of, 121; metamorphosis of, 139; yolk-sack of, 140; vertebral column of, 556

Pituitary body, of Rabbit, 231; general development of, 435; meaning of, 436; Placenta, of Salpa, 29; Elasmobranchii, 66; of Mammalia, 232; villi of, 235; deciduate and non-deciduate, 239; comparative account of, 239-259; characters of primitive type of, 240; zonary, 248; non-deciduate, 250; histology of, 257; evolution of, 259

Placoid scales, 395

Planorbis, excretory organs of, 681

Planula, structure of, 367

Pleural cavities, 631

Pleuronectidæ, development of, 80

Pneumatocoela, characters of, 327

Polygordius, excretory organs of, 684

Polyophthalmus, eye of, 479

Polypedates, brood-pouch of, 121

Polyzoa, excretory organs of, 682; generative cells of, 745; generative ducts of, 751

Pons Varolii, 426, 427

Pori abdominales, Ammocoetes, 99

Porifera, ancestral form of, 345; development of generative cells of, 741

Portal vein, 653

Postanal gut of Elasmobranchii, 58, 59, 60; Teleostei, 75; Chick, 169; general account of, 323, 772

Præmaxilla, 594

Præopercular bone, 593

Præoral lobe, ganglion of, 377, 380

Prefrontals, 597

Presphenoid region of skull, 570

Primitive groove of Chick, 155

Primitive streak, of Chick, 152, 161; meaning of, 153; origin of mesoblast form in Chick, 154; continuity of hypoblast with epiblast at anterior end of, in Chick, 156; comparison of with blastopore, 165; fate of, in Chick, 165; of Lacerta, 203; of Rabbit, 221; of Guinea-pig, 223; fusion of layers at, in Rabbit, 224; comparison of with blastopore of lower forms, 226, 287; of Mammalia, 290

Processus falciformis of Ammocoetes, 498; of Elasmobranch, 502; of Teleostei, 503

Proctodæum, 778

Pronephros, of Teleostei, 78, 701; Petromyzon, 95, 99, 700; Acipenser, 106, 110; Amphibia, 134, 707; general account of, 689; of Cyclostomata, 700; of Myxine, 701; Ganoidei, 705; of Amniota, 714; of Chick, 718; summary of and general conclusions as to, 728; relation of, to mesonephros, 731; cause of atrophy of, 729

Prootic, 596, 597

Propterygium, 616

Proteus, branchial arches of, 142

Protochordata, characters of, 327

Proto-ganoidei, characters of, 328

Proto-gnathostomata, characters of, 328

Proto-pentadactyloidei, characters of, 329

Protovertebrata, characters of, 328

Pseudis, Tadpole of, 139; vertebral column of, 556

Pseudophryne, yolk-sack of, 140; Tadpole of, 140

Pterygoid bone, of Teleostei, 581; origin of, 597

Pterygoquadrate bar, of Elasmobranchii, 576; of Teleostei, 581; Axolotl, 584; Frog, 584; of Sauropsida, 588; of Mammalia, 589

Pulmonary artery, origin of, 645; of Amphibia, 645; of Amniota, 649

Pulmonary vein, 655

Pupil, 489

Pyrosoma, development of, 23

Quadrate bone of Teleostei, 581; of Axolotl, 584; Frog, 585; Sauropsida, 588

Quadratojugal bone, 594

Rabbit, development of, 214; general growth of embryo of, 227; placenta of, 248

Radiate symmetry, passage from to bilateral symmetry, 373-376

Raja, caudal vertebræ of, 553

Rat, placenta of, 242

Recessus labyrinthi, 519

Reissner's membrane, 524

Reptilia, development of, 202; viviparous, 202; cerebellum of, 426; infundibulum of, 431; pituitary body of, 436; cerebrum of, 439; vertebral column of, 556; arterial system of, 648; venous system of, 656; mesonephros of, 713; testicular network of, 723; spermatozoa of, 747

Restiform tracts of Elasmobranchii and Teleostei, 425

Retina, histogenesis of, 490

Retinulæ, 482

Rhabdom, 482

Rhinoderma, brood-pouch of, 121; metamorphosis of, 139

Ribs, development of, 560

Rosenmüller's organ, 725

Rotifera, excretory organs of, 680

Round ligament of liver, 663

Ruminantia, placenta of, 253

Sacci vasculosi, 437

Sacculus hemisphericus, 519; of Mammals, 519, 520

Sagitta. _See_ 'Chætognatha'

Salpa, sexual development of, 29; asexual development of, 33

Salamandra, larva of, 142; vertebral column of, 553; limbs of, 619; mesonephros of, 708; Müllerian duct of, 710

Salmonidæ, hypoblast of, 71; generative ducts of, 704

Sauropsida, gastrula of, 286; meaning of primitive streak of, 288; blastopore of, 289; mandibular and hyoid arches of, 588; pectoral girdle of, 601

Scala, vestibuli, 522; tympani, 523; media, 522

Scales, general development of, 396; development of placoid scales, 395

Scapula, 599

Sclerotic, 488

Scrotum, development of, 727

Scyllium, caudal vertebræ of, 553; mandibular and hyoid arches of, 578; pectoral girdle of, 600; limbs of, 610; pelvic fin of, 614; pectoral fin of, 615

Segmental duct, 690; development of in Elasmobranchs, 690; of Cyclostomata, 700; of Teleostei, 701; of Ganoidei, 704, 705; of Amphibia, 707; of Amniota, 713

Segmental organs, 682

Segmental tubes, 690; development of in Elasmobranchs, 691; rudimentary anterior in Elasmobranchs, 693; development of secondary, 731

Segmentation cavity, of Elasmobranchii, 42-44; Teleostei, 69, 85, 86; Amphibia, 122, 125

Segmentation, meaning of, 331

Segmentation of ovum, in Amphioxus, 2; Ascidia, 9; Molgula, 22; Pyrosoma, 23; Salpa, 30; Elasmobranchii, 40; Telostei, 69; Petromyzon, 84; Acipenser, 102; Lepidosteus, 111; Amphibia, 122, 124; Newt, 125; Chick, 146; Lizard, 202; Rabbit, 214

Semicircular canals, 519

Sense organs, comparative account of development of, 304

Septum lucidum, 443

Serous membrane, Lacerta, 209; of Rabbit, 237

Seventh nerve, development of, 459

Shell-gland of Crustacea, 689

Shield, embryonic, of Chick, 151; of Lacerta, 202

Simiadæ, placenta of, 247

Sinus rhomboidalis, of Chick, 162

Sinus venosus, 637

Sirenia, placenta of, 255

Sixth nerve, 463

Skate, mandibular and hyoid arches of, 577

Skeleton, elements of found in Vertebrata, 542

Skull, general development of, 564; historical account of, 564; development of cartilaginous, 566; cartilaginous walls of, 570; composition of primitive cartilaginous cranium, 565

Somatopleure, of Chick, 170

Spelerpes, branchial arches of, 142

Spermatozoa, of Porifera, 741; of Vertebrata, 746

Sphenoid bone, 595

Sphenodon, hyoid arch of, 588

Spinal cord, general account of, 415; white matter of, 415; central canal of, 417, 418; commissures of, 417; grey matter of, 417; fissures of, 418

Spinal nerves, posterior roots of, 449; anterior roots of, 453

Spiracle, of Elasmobranchii, 62; Acipenser, 105; Amphibia, 136

Spiral valve. _See_ 'Valve'

Spleen, 664

Splenial bone, 595

Squamosal bone, 593

Stapes, 529; of Mammal, 590

Sternum, development of, 562

Stolon of Doliolum, 29; Salpa, 33

Stomodæum, 774

Stria vascularis, 524

Styloid process, 591

Subintestinal vein, 651; meaning of, 651

Syngnathus, brood-pouch of, 68

Subnotochordal rod, of Elasmobranchii, 54; Petromyzon, 94; Acipenser, 110; Lepidosteus, 115; general account of, 754; comparison of with siphon of Chætopods, 756

Subzonal membrane, 237; villi of, 236

Sulcus of Munro, 432

Supraclavicle, 600

Suprarenal bodies, 664

Supra-temporal bone, 593

Swimming bladder, _see_ Air bladder

Sylvian aqueduct, 428

Sylvian fissure, 444

Sympathetic ganglia, development of, 467

Tadpole, 134, 139, 140; phylogenetic meaning of, 137; metamorphosis of, 137; meaning of suctorial mouth of, 585

Tail of Teleostei, 80; Acipenser, 109; Lepidosteus, 109; Amphibia, 132

Tarsus, development of, 620

Teeth, horny provisional, of Amphibia, 136; general development of, 776; origin of, 777

Teleostei, development of, 68; viviparous, 68; comparison of formation of layers in, 286; restiform tracts of, 425; mid-brain of, 425; infundibulum of, 431; cerebrum of, 439; nares of, 534; lateral line of, 538; notochord and membrana elastica of, 549; vertebral column of, 553; ribs of, 561; hyoid and mandibular arches of, 579; pectoral girdle of, 601; pelvic girdle of, 606; limbs of, 618; heart of, 637; arterial system of, 645; muscle-plates of, 670; excretory organs of, 701; generative ducts of, 704, 735, 749; swimming bladder of, 763; postanal gut of, 774

Teredo, nervous system of, 414

Test of Ascidia, 14; Salpa, 31

Testicular network, of Elasmobranchs, 697; of Amphibia, 712; Reptilia, 723; of Mammals, 724

Testis of Vertebrata, 746

Testis, connection of with Wolffian body, in Elasmobranchii, 697; in Amphibia, 710; in Amniota, 723; origin of, 735

Thalamencephalon of Chick, 175; general development of, 430

Third nerve, development of, 461

Thymus gland, 762

Thyroid gland, Petromyzon, 92; general account of, 759; nature of, 760; development of in Vertebrata, 761

Tooth. _See_ 'Teeth'

Tori semicirculares, 428

Tornaria, 372

Trabeculæ, 565, 567; nature of, 568

Trachea, 766

Trematoda, excretory organs of, 681

Triton alpestris, sexual larva of, 143

Triton, development of limbs of, 619; urinogenital organs of, 712

Truncus arteriosus, 638; of Amphibia, 638; of Birds, 639

Tunicata, development of mesoblast of, 293; test of, 394; eye of, 507; auditory organ of, 530; olfactory organ of, 532; generative duct of, 749; intestine of 767; postanal gut of, 771; stomodæum of, 775

Turbellaria, excretory organs of, 681

Tympanic annulus of Frog, 587

Tympanic cavity, of Amphibia, 135; Chick, 180; Rabbit, 232; general development of, 528; of Mammals, 591

Tympanic membrane, of Chick, 180; general development of, 528

Tympanohyal, 591

Umbilical canal of Elasmobranchii, 54, 57, 58, 59

Umbilical cord, 238; vessels of, 239

Ungulata, placenta of, 250

Urachus, 239, 726

Ureters, of Elasmobranchii, 696; development of, 723

Urethra, 727

Urinary bladder of Amphibia, 712; of Amniota, 726

Urinogenital organs, _see_ Excretory organs

Urinogenital sinus of Petromyzon, 700; of Sauropsida, 726; of Mammalia, 727

Urochorda, development of, 9

Uterus, development of, 726; of Marsupials, 726

Uterus masculinus, 726

Utriculus, 519

Uvea of iris, 489

Vagus nerve, development of, 456, 457; intestinal branch of, 458; branch of to lateral line, 459

Valve, spiral, of Petromyzon, 97; Acipenser, 110; general account of, 767

Valves, semilunar, 641; auriculo-ventricular, 642

Vasa efferentia, of Elasmobranchs, 697; of Amphibia, 711; general origin of, 724

Vascular system, of Amphioxus, 8; Petromyzon, 97; Lepidosteus, 116; general development of, 632

Vas deferens, of Elasmobranchii, 697; of Amniota, 723

Vein, subintestinal of Petromyzon, 97; Acipenser, 110; Lepidosteus, 116

Velum of Petromyzon, 91

Vena cava inferior, development of, 655

Venous system of Petromyzon, 97; general development of, 651; of Fishes, 651; of Amphibia and Amniota, 655; of Reptilia, 656; of Ophidia, 656; of Aves, 658; of Mammalia, 661

Ventricle, fourth, of Chick, 176; history of, 424

Ventricle, lateral, 438, 440; fifth, 443

Ventricle, third, of Chick, 175

Vertebral bodies, of Chick, 183

Vertebral column, development of, 545, 549; epichordal and perichordal development of in Amphibia, 556

Vespertilionidæ, early development of, 217

Vieussens, valve of, 426

Villi, placental, of zona radiata, 235; subzonal membrane, 235; chorion, 237; Man, 246; comparative account of, 257; of young human ovum, 265, 269

Visceral arches, Amphioxus, 7; Elasmobranchii, 57-60; Teleostei, 77; Acipenser, 106; Lepidosteus, 116; Amphibia, 133; Chick, 177; Rabbit, 231; præoral, 570; relation of to head cavities, 572; disappearance of posterior, 573; dental plates of in Teleostei, 574

Visual organs, evolution of, 470

Vitelline arteries of Chick, 195

Vitelline veins of Chick, 195

Vitreous humour, of Ammocoetes, 98; general development of, 494; blood-vessels of in Mammals 503; mesoblastic ingrowth in Mammals, 503

Vomer, 594

White matter, of spinal cord, 415; of brain, 423

Wolffian body, _see_ 'Mesonephros'

Wolffian duct, first appearance of in Chick, 183; general account of, 690; of Elasmobranchs, 693; of Ganoids, 704; of Amphibia, 710; of Amniota, 713; atrophy of in Amniota, 724

Wolffian ridge, 185

Yolk blastopore, of Elasmobranchii, 64

Yolk, folding off of embryo from, in Elasmobranchii, 55; in Teleostei, 76; Acipenser, 106; Chick, 168, 170

Yolk nuclei, of Elasmobranchii, 41, 53; Teleostei, 69, 75

Yolk, of Elasmobranchii, 40; Teleostei, 68; Petromyzon, 96; Acipenser, 109; Amphibia, 122, 129; Chick, 146; influence of on formation of layers, 278; influence of on early development, 341, 342

Yolk-sack, Amphibia, 131, 140, 141; enclosure of, 123

Yolk-sack, development of in Rabbit, 227; of Mammalia reduced, 227; circulation of in Rabbit, 233; enclosure of in Sauropsida, 289

Yolk-sack, enclosure of, Petromyzon, 86

Yolk-sack, Lepidosteus, 118

Yolk-sack of Chick, enclosure of, 160; stalk of, 174; general account of, 193; circulation of, 195; later history of, 198

Yolk-sack of Elasmobranchii, enclosure of, 62, 283; circulation of, 64

Yolk-sack of Lacerta, 209; circulation of, 209

Yolk-sack, Teleostei, 75, 81; enclosure of, 75; circulation of, 81

Zona radiata, villi of, 237

Zonula of Zinn, 495

BIBLIOGRAPHY.

CEPHALOPODA.

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(2) A. Kowalevsky. "Weitere Studien über die Entwicklungsgeschichte des Amphioxus lanceolatus." _Archiv f. mikr. Anat._, Vol. XIII. 1877.

(3) Leuckart u. Pagenstecher. "Untersuchungen über niedere Seethiere." _Müller's Archiv_, 1858.

(4) Max Schultze. "Beobachtung junger Exemplare von Amphioxus." _Zeit. f. wiss. Zool._, Bd. III. 1851.

(5) A. M. Marshall. "On the mode of Oviposition of Amphioxus." _Jour. of Anat. and Phys._, Vol. X. 1876.

UROCHORDA.

(6) P. J. van Beneden. "Recherches s. l'Embryogénie, l'Anat. et la Physiol. des Ascidies simples." _Mém. Acad. Roy. de Belgique_, Tom. XX.

(7) W. K. Brooks. "On the development of Salpa." _Bull. of the Museum of Comp. Anat. at Harvard College, Cambridge, Mass._

(8) H. Fol. _Etudes sur les Appendiculaires du détroit de Messine._ Genève et Bâle, 1872.

(9) Ganin. "Neue Thatsachen a. d. Entwicklungsgeschichte d. Ascidien." _Zeit. f. wiss. Zool._, Vol. XX. 1870.

(10) C. Gegenbaur. "Ueber den Entwicklungscyclus von Doliolum nebst Bemerkungen über die Larven dieser Thiere." _Zeit. f. wiss. Zool._, Bd. VII. 1856.

(11) A. Giard. "Etudes critiques des travaux d'embryogénie relatifs à la parenté des Vertébrés et des Tuniciers." _Archiv Zool. expériment._, Vol. I. 1872.

(12) A. Giard. "Recherches sur les Synascidies." _Archiv Zool. expér._, Vol. I. 1872.

(13) O. Hertwig. "Untersuchungen üb. d. Bau u. d. Entwicklung des Cellulose-Mantels d. Tunicaten." _Jenaische Zeitschrift_, Bd. VII. 1873.

(14) Th. H. Huxley. "Remarks upon Appendicularia and Doliolum." _Phil. Trans._, 1851.

(15) Th. H. Huxley. "Observations on the anatomy and physiology of Salpa and Pyrosoma." _Phil. Trans._, 1851.

(16) Th. H. Huxley. "Anatomy and development of Pyrosoma." _Linnean Trans._, 1860, Vol. XXIII.

(17) Keferstein u. Ehlers. _Zoologische Beiträge_, 1861. Doliolum.

(18) A. Kowalevsky. "Entwicklungsgeschichte d. einfachen Ascidien." _Mém. Acad. Pétersbourg_, VII. série, T. X. 1866.

(19) A. Kowalevsky. "Beitrag z. Entwick. d. Tunicaten." _Nachrichten d. königl. Gesell. zu Göttingen._ 1868.

(20) A. Kowalevsky. "Weitere Studien üb. d. Entwicklung d. einfachen Ascidien." _Archiv f. mikr. Anat._, Vol. VII. 1871.

(21) A. Kowalevsky. "Ueber Knospung d. Ascidien." _Archiv f. mikr. Anat._, Vol. X. 1874.

(22) A. Kowalevsky. "Ueber die Entwicklungsgeschichte d. Pyrosoma." _Archiv f. mikr. Anat._, Vol. XI. 1875.

(23) A. Krohn. "Ueber die Gattung Doliolum u. ihre Arten." _Archiv f. Naturgeschichte_, Bd. XVIII. 1852.

(24) A. Krohn. "Ueber die Entwicklung d. Ascidien." _Müller's Archiv_, 1852.

(25) A. Krohn. "Ueber die Fortpflanzungsverhältnisse d. Botrylliden." _Archiv f. Naturgeschichte_, Vol. XXXV. 1869.

(26) A. Krohn. "Ueber die früheste Bildung d. Botryllenstöcke." _Archiv f. Naturgeschichte_, Vol. XXXV. 1869.

(27) C. Kupffer. "Die Stammverwandschaft zwischen Ascidien u. Wirbelthieren." _Archiv f. mikr. Anat._, Vol. VI. 1870.

(28) C. Kupffer. "Zur Entwicklung d. einfachen Ascidien." _Archiv f. mikr. Anat._, Vol. VIII. 1872.

(29) H. Lacaze Duthiers. "Recherches sur l'organisation et l'Embryogénie des Ascidies (Molgula tubulosa)." _Comptes rendus_, May 30, 1870, p. 1154.

(30) H. Lacaze Duthiers. "Les Ascidies simples des Côtes de France" (Development of Molgula). _Archiv Zool. expér._, Vol. III. 1874.

(31) R. Leuckart. "Salpa u. Verwandte." _Zoologische Untersuchungen_, Heft II.

(32) E. Metschnikoff. "Observations sur le développement de quelques animaux (Botryllus and Simple Ascidians)." _Bull. d. l'Acad. Pétersbourg_, Vol. XIII. 1869.

(33) H. Milne-Edwards. "Observations s. l. Ascidies composées des côtes de la Manche." _Mémoires d. l'Institut_, T. XVIII. 1842.

(34) W. Salensky. "Ueber d. embryonale Entwicklungsgeschichte der Salpen." _Zeit. f. wiss. Zool._, B. XXVII. 1877.

(35) W. Salensky. "Ueber die Knospung d. Salpen." _Morphol. Jahrbuch_, Bd. III. 1877.

(36) W. Salensky. "Ueber die Entwicklung d. Hoden u. über den Generationswechsel d. Salpen." _Zeit. f. wiss. Zool._, Bd. XXX. Suppl. 1878.

(37) C. Semper. "Ueber die Entstehung d. geschichteten Cellulose-Epidermis d. Ascidien." _Arbeit. a. d. zool.-zoot. Instit. Würzburg_, Vol. II. 1875.

(38) Fr. Todaro. _Sopra lo sviluppo e l'anatomia delle Salpe._ Roma, 1875.

(39) Fr. Todaro. "Sui primi fenomeni dello sviluppo delle Salpe." _Reale Accademia dei Lincei_, Vol. IV. 1880.

ELASMOBRANCHII.

(40) F. M. Balfour. "A preliminary account of the development of the Elasmobranch Fishes." _Quart. J. of Micr. Science_, Vol. XIV. 1876.

(41) F. M. Balfour. "A Monograph on the development of Elasmobranch Fishes." London, 1878. Reprinted from the _Journal of Anat. and Physiol._ for 1876, 1877, and 1878.

(42) Z. Gerbe. "_Recherches sur la segmentation de la cicatrule et la formation des produits adventifs de l'oeuf des Plagiostomes et particuliérement des Raies._" Vide also _Journal de l'Anatomie et de la Physiologie_, 1872.

(43) W. His. "Ueb. d. Bildung v. Haifischenembryonen." _Zeit. für Anat. u. Entwick._, Vol. II. 1877.

(44) A. Kowalevsky. "Development of Acanthias vulgaris and Mustelus lævis." (Russian.) _Transactions of the Kiew Society of Naturalists_, Vol. I. 1870.

(45) R. Leuckart. "Ueber die allmählige Bildung d. Körpergestalt bei d. Rochen." _Zeit. f. wiss. Zool._, Bd. II., p. 258.

(46) Fr. Leydig. _Rochen u. Haie._ Leipzig, 1852.

(47) A. W. Malm. "Bidrag till kännedom om utvecklingen af Rajæ." _Kongl. vetenskaps akademiens forhandlingar._ Stockholm, 1876.

(48) Joh. Müller. _Glatter Haie des Aristoteles und über die Verschiedenheiten unter den Haifischen und Rochen in der Entwicklung des Eies._ Berlin, 1840.

(49) S. L. Schenk. "Die Eier von Raja quadrimaculata innerhalb der Eileiter." _Sitz. der k. Akad. Wien_, Vol. LXXIII. 1873.

(50) Alex. Schultz. "Zur Entwicklungsgeschichte des Selachiereies." _Archiv für micro._ Anat., Vol. XI. 1875.

(51) Alex. Schultz. "Beitrag zur Entwicklungsgeschichte d. Knorpelfische." _Archiv für micro. Anat._, Vol. XIII. 1877.

(52) C. Semper. "Die Stammesverwandschaft d. Wirbelthiere u. Wirbellosen." _Arbeit. a. d. zool.-zoot. Instit. Würzburg_, Vol. II. 1875.

(53) C. Semper. "Das Urogenitalsystem d. Plagiostomen, etc." _Arbeit. a. d. zool.-zoot. Instit. Würzburg_, Vol. II. 1875.

(54) Wyman. "Observations on the Development of Raja batis." _Memoirs of the American Academy of Arts and Sciences_, Vol. IX. 1864.

TELEOSTEI.

(55) Al. Agassiz. "On the young Stages of some Osseous Fishes. I. Development of the Tail." _Proceedings of the American Academy of Arts and Sciences_, Vol. XIII. Presented Oct. 11, 1877.

(56) Al. Agassiz. "II. Development of the Flounders." _Proceedings of the American Acad. of Arts and Sciences_, Vol. XIV. Presented June, 1878.

(57) K. E. v. Baer. _Untersuchungen über die Entwicklungsgeschichte der Fische._ Leipzig, 1835.

(58) Ch. van Bambeke. "Premiers effets de la fécondation sur les oeufs de Poissons: sur l'origine et la signification du feuillet muqueux on glandulaire chez les Poissons Osseux." _Comptes Rendus des Séances de l'Académie des Sciences_, Tome LXXIV. 1872.

(59) Ch. van Bambeke. "Recherches sur l'Embryologie des Poissons Osseux." _Mém. couronnés et Mém. de savants étrangers de l'Académie roy. Belgique_, Vol. XL. 1875.

(60) E. v. Beneden. "A contribution to the history of the Embryonic development of the Teleosteans." _Quart. J. of Micr. Sci._, Vol. XVIII. 1878.

(61) E. Calberla. "Zur Entwicklung des Medullarrohres u. d. Chorda dorsalis d. Teleostier u. d. Petromyzonten." _Morphologisches Jahrbuch_, Vol. III. 1877.

(62) A. Götte. "Beiträge zur Entwicklungsgeschichte der Wirbelthiere." _Archiv f. mikr. Anat._, Vol. IX. 1873.

(63) A. Götte. "Ueber d. Entwicklung d. Central-Nervensystems der Teleostier." _Archiv f. mikr. Anat._, Vol. XV. 1878.

(64) A. Götte. "Entwick. d. Teleostierkeime." _Zoologischer Anzeiger_, No. 3. 1878.

(65) W. His. "Untersuchungen über die Entwicklung von Knochenfischen, etc." _Zeit. f. Anat. u. Entwicklungsgeschichte_, Vol. I. 1876.

(66) W. His. "Untersuchungen über die Bildung des Knochenfischembryo (Salmen)." _Archiv f. Anat. u. Physiol._, 1878.

(67) E. Klein. "Observations on the early Development of the Common Trout." _Quart. J. of Micr. Science_, Vol. XVI. 1876.

(68) C. Kupffer. "Beobachtungen über die Entwicklung der Knochenfische." _Archiv f. mikr. Anat._, Bd. IV. 1868.

(69) C. Kupffer. _Ueber Laichen u. Entwicklung des Ostsee-Herings._ Berlin, 1878.

(70) M. Lereboullet. "Recherches sur le développement du brochet de la perche et de l'écrevisse." _Annales des Sciences Nat._, Vol. I., Series IV. 1854.

(71) M. Lereboullet. "Recherches d'Embryologie comparée sur le développement de la Truite." _An. Sci. Nat._, quatrième série, Vol. XVI. 1861.

(72) T. Oellacher. "Beiträge zur Entwicklungsgeschichte der Knochenfische nach Beobachtungen am Bachforellenei." _Zeit. f. wiss. Zool._, Vol. XXII., 1872, and Vol. XXIII., 1873.

(72[A]) H. Rathke. _Abh. z. Bildung u. Entwick. d. Menschen u. Thiere._ Leipzig, 1832-3. Part II. Blennius.

(73) Reineck. "Ueber die Schichtung des Forellenkeims." _Archiv f. mikr. Anat._, Bd. V. 1869.

(74) S. Stricker. "Untersuchungen über die Entwicklung der Bachforelle." _Sitzungsberichte der Wiener k. Akad. d. Wiss._, 1865. Vol. LI. Abth. 2.

(75) Carl Vogt. "Embryologie des Salmones." _Histoire Naturelle des Poissons de l'Europe Centrale._ L. Agassiz. 1842.

(76) C. Weil. "Beiträge zur Kenntniss der Knochenfische." _Sitzungsber. der Wiener kais. Akad. der Wiss._, Bd. LXVI. 1872.

CYCLOSTOMATA.

(77) E. Calberla. "Der Befruchtungsvorgang beim Petromyzon Planeri." _Zeit. f. wiss. Zool._, Vol. XXX. 1877.

(78) E. Calberla. "Ueb. d. Entwicklung d. Medullarrohres u. d. Chorda dorsalis d. Teleostier u. d. Petromyzonten." _Morpholog. Jahrbuch_, Vol. III. 1877.

(79) C. Kupffer u. B. Benecke. _Der Vorgang d. Befruchtung am Ei d. Neunaugen._ Königsberg, 1878.

(80) Aug. Müller. "Ueber die Entwicklung d. Neunaugen." Müller's _Archiv_, 1856.

(81) Aug. Müller. _Beobachtungen üb. d. Befruchtungserscheinungen im Ei d. Neunaugen._ Königsberg, 1864.

(82) W. Müller. "Das Urogenitalsystem d. Amphioxus u. d. Cyclostomen." _Jenaische Zeitschrift_, Vol. IX. 1875.

(83) Ph. Owsjannikoff. "Die Entwick. von d. Flussneunaugen." Vorläuf. Mittheilung. _Mélanges Biologiques tirés du Bulletin de l'Acad. Imp. St Pétersbourg_, Vol. VII. 1870.

(84) Ph. Owsjannikoff. _On the development of Petromyzon fluviatilis_ (Russian).

(85) Anton Schneider. _Beiträge z. vergleich. Anat. u. Entwick. d. Wirbelthiere._ Quarto. Berlin, 1879.

(86) M. S. Schultze. "Die Entwickl. v. Petromyzon Planeri." Gekrönte Preisschrist. Haarlem, 1856.

(87) W. B. Scott. "Vorläufige Mittheilung üb. d. Entwicklungsgeschichte d. Petromyzonten." _Zoologischer Anzeiger_, Nos. 63 and 64. III. Jahrg. 1880.

GANOIDEI.

_Acipenseridæ._

(88) Knock. "Die Beschr. d. Reise z. Wolga Behufs d. Sterlettbefruchtung." _Bull. Soc. Nat._ Moscow, 1871.

(89) A. Kowalevsky, Ph. Owsjannikoff, and N. Wagner. "Die Entwick. d. Störe." Vorläuf. Mittheilung. _Mélanges Biologiques tirés du Bulletin d. l'Acad. Imp. St Pétersbourg_, Vol. VII. 1870.

(90) W. Salensky. "Development of the Sterlet (Acipenser ruthenus)." 2 Parts. _Proceedings of the Society of Naturalists in the imperial University of Kasan._ 1878 and 9 (Russian). Part I., abstracted in Hoffmann and Schwalbe's _Jahresbericht_ for 1878.

(91) W. Salensky. "Zur Embryologie d. Ganoiden (Acipenser)." _Zoologischer Anzeiger_, Vol. I., Nos. 11, 12, 13.

_Lepidosteidæ._

(92) Al. Agassiz. "The development of Lepidosteus." _Proc. Amer. Acad. of Arts and Sciences_, Vol. XIII. 1878.

AMPHIBIA.

(93) Ch. van Bambeke. "Recherches sur le développement du Pélobate brun." _Mémoires couronnés, etc. de l'Acad. roy. de Belgique_, 1868.

(94) Ch. van Bambeke. "Recherches sur l'embryologie des Batraciens." _Bulletin de l'Acad. roy. de Belgique_, 1875.

(95) Ch. van Bambeke. "Nouvelles recherches sur l'embryologie des Batraciens." _Archives de Biologie_, Vol. I. 1880.

(96) K. E. von Baer. "Die Metamorphose des Eies der Batrachier." Müller's _Archiv_, 1834.

(97) B. Benecke. "Ueber die Entwicklung des Erdsalamanders." _Zoologischer Anzeiger_, 1880.

(98) S. F. Clarke. "Development of Amblystoma punctatum," Part I., External. _Studies from the Biological Laboratory of the Johns Hopkins University_, No. II. 1880.

(99) H. Cramer. "Bemerkungen üb. d. Zellenleben in d. Entwick. d. Froscheies." Müller's _Archiv_, 1848.

(100) A. Ecker. _Icones Physiolog._ 1851-1859.

(101) A. Götte. _Die Entwicklungsgeschichte der Unke._ Leipzig, 1875.

(102) C. K. Hoffmann. "Amphibia." _Klassen u. Ordnungen d. Thierreichs_, 1873-1879.

(103) T. H. Huxley. Article "Amphibia" in the _Encyclopædia Britannica_.

(104) A. Moquin-Tandon. "Développement des Batraciens anures." _Annales des Sciences Naturelles_, III. 1875.

(105) G. Newport. "On the impregnation of the Ovum in Amphibia" (three memoirs). _Phil. Trans._ 1851, 1853, and 1854.

(106) W. K. Parker. "On the structure and development of the Skull of the common Frog." _Phil. Trans._, CLXI. 1871.

(107) W. K. Parker. "On the structure and development of the Skull of the Batrachia." _Phil. Trans._, Vol. CXLVI., Part 2. 1876.

(108) W. C. H. Peters. "Ueber die Entwicklung der Coecilien und besonders von Coecilia compressicauda." _Berlin. Monatsbericht_, p. 40, 1874.

(109) W. C. H. Peters. "Ueber die Entwicklung der Coecilien." _Berl. Monatsbericht_, p. 483, 1875.

(110) J. L. Prevost and J. B. Dumas. "Deuxième Mém. s. l. génération. Développement de l'oeuf d. Batraciens." _Ann. Sci. Nat._ II. 1824.

(111) R. Remak. _Untersuchungen über die Entwicklung der Wirbelthiere_, 1850-1858.

(112) M. Rusconi. _Développement de la grenouille commune depuis le moment de sa naissance jusqu'à son état parfait_, 1826.

(113) M. Rusconi. _Histoire naturelle, développement et métamorphose de la Salamandre terrestre_, 1854.

(114) W. B. Scott and H. F. Osborn. "On the early development of the common Newt." _Quart. J. of Micr. Science_, Vol. XXIX. 1879.

(115) S. Stricker. "Entwicklungsgeschichte von Bufo cinereus." _Sitzb. der kaiserl. Acad. zu Wien_, 1860.

(116) S. Stricker. "Untersuchungen über die ersten Anlagen in Batrachier-Eiern." _Zeitschrift f. wiss. Zoologie_, Bd. XI. 1861.

AVES.

(117) K. E. von Baer. _Ueb. Entwicklungsgeschichte d. Thiere._ Königsberg, 1828-1837.

(118) F. M. Balfour. "The development and growth of the layers of the Blastoderm," and "On the disappearance of the Primitive Groove in the Embryo Chick." _Quart. J. of Micros. Science_, Vol. XIII. 1873.

(119) M. Braun. "Die Entwicklung d. Wellenpapagei's." Part I. _Arbeit. d. zool.-zoot. Instit. Würzburg._ Vol. V. 1879.

(120) M. Braun. "Aus d. Entwick. d. Papageien; I. Rückenmark; II. Entwicklung d. Mesoderms; III. Die Verbindungen zwischen Rückenmark u. Darm bei Vögeln." _Verh. d. phys.-med. Ges. zu Würzburg._ N. F. Bd. XIV. and XV. 1879 and 1880.

(121) J. Disse. "Die Entwicklung des mittleren Keimblattes im Hühnerei." _Archiv für mikr. Anat._, Vol. XV. 1878.

(122) J. Disse. "Die Entstehung d. Blutes u. d. ersten Gefässe im Hühnerei." _Archiv f. mikr. Anat._, Vol. XVI. 1879.

(123) Fr. Durante. "Sulla struttura della macula germinativa delle uova di Gallina." _Ricerche nel Laboratorio di Anatomia della R. Università di Roma._

(124) E. Dursy. _Der Primitivstreif des Hühnchens._ 1867.

(125) M. Duval. "Etude sur la ligne primitive de l'embryon de Poulet." _Annales des Sciences Naturelles_, Vol. VII. 1879.

(126) M. Foster and F. M. Balfour. _Elements of Embryology._ Part I. London, 1874.

(127) Gasser. "Der Primitivstreifen bei Vogelembryonen." _Schriften d. Gesell. zur Beförd. d. gesammten Naturwiss. zu Marburg_, Vol. II. Supplement I. 1879.

(128) A. Götte. "Beiträge zur Entwicklungsgeschichte d. Wirbelthiere. II. Die Bildung d. Keimblatter u. d. Blutes im Hühnerei." _Archiv für mikr. Anat._, Vol. X. 1874.

(129) V. Hensen. "Embryol. Mitth." _Archiv f. mikr. Anat._, Vol. III. 1867.

(130) W. His. _Untersuch. üb. d. erste Anlage d. Wirbelthierleibes._ Leipzig, 1868.

(131) W. His. _Unsere Körperform and das physiol. Problem ihrer Entstehung._ Leipzig, 1875.

(132) W. His. "Der Keimwall des Hühnereies u. d. Entstehung d. parablastischen Zellen." _Zeit. f. Anat. u. Entwicklungsgeschichte._ Bd. I. 1876.

(133) W. His. "Neue Untersuchungen üb. die Bildung des Hühnerembryo I." _Archiv f. Anat. u. Phys._ 1877.

(134) E. Klein. "Das mittiere Keimblatt in seiner Bezieh. z. Entwick. d. ers. Blutgefässe und Blutkörp. im Hühnerembryo." _Sitzungsber. Wien. Akad._, Vol. LXIII. 1871.

(135) A. Kölliker. _Entwicklungsgeschichte d. Menschen u. d. höheren Thiere._ Leipzig, 1879.

(136) C. Kupffer. "Die Entsteh. d. Allantois u. d. Gastrula d. Wirbelth." _Zoolog. Anzeiger_, Vol. II. 1879, pp. 520, 593, 612.

(137) C. Kupffer and B. Benecke. "Photogramme z. Ontogenie d. Vögel." _Nov. Act. d. k. Leop.-Carol.-Deutschen Akad. d. Naturforscher_, Vol. XLI. 1879.

(138) J. Oellacher. "Untersuchungen über die Furchung u. Blatterbildung im Hühnerei." _Stricker's Studien._ 1870.

(139) C. H. Pander. _Beiträge z. Entwick. d. Hühnchens im Eie._ Würzburg, 1817.

(140) A. Rauber. "Ueber die Embryonalanlage des Hühnchens." _Centralblatt für d. medic. Wissenschaften._ 1874-75.

(141) A. Rauber. _Ueber die Stellung des Hühnchens im Entwicklungsplan._ 1876.

(142) A. Rauber. "Primitivrinne und Urmund. Beiträge zur Entwicklungsgeschichte des Hühnchens." _Morphol. Jahrbuch_, B. II. 1876.

(143) A. Rauber. _Primitivstreifen und Neurula der Wirbelthiere in normaler und pathologischer Beziehung._ 1877.

(144) R. Remak. _Untersuch. üb. d. Entwicklung d. Wirbelthiere._ Berlin, 1850-55.

(145) S. L. Schenk. "Beiträge z. Lehre v. d. Organanlage im motorischen Keimblatt." _Sitz. Wien. Akad._, Vol. LVII. 1860.

(146) S. L. Schenk. "Beiträge z. Lehre v. Amnion." _Archiv f. mikr. Anat._, Vol. VII. 1871.

(147) S. L. Schenk. _Lehrbuch d. vergleich. Embryol. d. Wirbelthiere._ Wien, 1874.

(148) S. Stricker. "Mittheil. üb. d. selbstständigen Bewegungen embryonaler Zellen." _Sitz. Wien. Akad._, Vol. XLIX. 1864.

(149) S. Stricker. "Beiträge zur Kenntniss des Hühnereies." _Wiener Sitzungsber._, Vol. LIV. 1866.

(150) H. Virchow. _Ueber d. Epithel d. Dottersackes im Hühnerei._ Inaug. Diss. Berlin, 1875.

(151) W. Waldeyer. "Ueber die Keimblätter und den Primitivstreifen bei der Entwicklung des Hühnerembryo." _Zeitschrift für rationelle Medicin._ 1869.

(152) C. F. Wolff. _Theoria generationis._ Halæ, 1759.

(153) C. F. Wolff. _Ueb. d. Bildung d. Darmcanals im bebrüteten Hünchen._ Halle, 1812.

REPTILIA.

(154) C. Kupffer and Benecke. _Die erste Entwicklung am Ei d. Reptilien._ Königsberg, 1878.

(155) C. Kupffer. "Die Entstehung d. Allantois u. d. Gastrula d. Wirbelthiere." _Zoologischer Anzeiger_, Vol. II. 1879, pp. 520, 593, 612.

_Lacertilia._

(156) F. M. Balfour. "On the early Development of the Lacertilia, together with some observations, etc." _Quart. J. of Micr. Science_, Vol. XIX. 1879.

(157) Emmert u. Hochstetter. "Untersuchung üb. d. Entwick. d. Eidechsen in ihren Eiern." Reil's _Archiv_, Vol. X. 1811.

(158) M. Lereboullet. "Développement de la Truite, du Lézard et du Limnée. II. Embryologie du Lézard." _An. Sci. Nat._, Ser. IV., Vol. XXVII. 1862.

(159) W. K. Parker. "Structure and Devel. of the Skull in Lacertilia." _Phil. Trans._, Vol. 170, p. 2. 1879.

(160) H. Strahl. "Ueb. d. Canalis myeloentericus d. Eidechse." _Schrift. d. Gesell. z. Beför. d. gesam. Naturwiss._ Marburg. July 23, 1880.

_Ophidia._

(161) H. Dutrochet. "Recherches s. l. enveloppes du foetus." _Mém. d. Soc. Méd. d'Emulation_, Paris, Vol. VIII. 1816.

(162) W. K. Parker. "On the skull of the common Snake." _Phil. Trans._, Vol. 169, Part II. 1878.

(163) H. Rathke. _Entwick. d. Natter._ Königsberg, 1839.

_Chelonia._

(164) L. Agassiz. _Contributions to the Natural History of the United States_, Vol. II. 1857. _Embryology of the Turtle._

(165) W. K. Parker. "On the development of the skull and nerves in the green Turtle." _Proc. of the Roy. Soc._, Vol. XXVIII. 1879. _Vide_ also _Nature_, April 14, 1879, and _Challenger Reports_, Vol. I. 1880.

(166) H. Rathke. _Ueb. d. Entwicklung d. Schildkröten._ Braunschweig, 1848.

_Crocodilia._

(167) H. Rathke. _Ueber die Entwicklung d. Krokodile._ Braunschweig, 1866.

MAMMALIA.

(168) K. E. von Baer. _Ueb. Entwicklungsgeschichte d. Thiere._ Königsberg, 1828-1837.

(169) Barry. "Researches on Embryology." First Series. _Philosophical Transactions_, 1838, Part II. Second Series, Ibid. 1839, Part II. Third Series, Ibid. 1840.

(170) Ed. van Beneden. _La maturation de l'oeuf, la fécondation et les premières phases du développement embryonaire d. Mammifères._ Bruxelles, 1875.

(171) Ed. van Beneden. "Recherches sur l'embryologie des Mammifères." _Archives de Biologie_, Vol. I. 1880.

(172) Ed. v. Beneden and Ch. Julin. "Observations sur la maturation etc. de l'oeuf chez les Cheiroptères." _Archives de Biologie_, Vol. I. 1880.

(173) Th. L. W. Bischoff. _Entwicklungsgeschichte d. Säugethiere u. des Menschen._ Leipzig, 1842.

(174) Th. L. W. Bischoff. _Entwicklungsgeschichte des Kanincheneies._ Braunschweig, 1842.

(175) Th. L. W. Bischoff. _Entwicklungsgeschichte des Hundeeies._ Braunschweig, 1845.

(176) Th. L. W. Bischoff. _Entwicklungsgeschichte des Meerschweinchens._ Giessen. 1852.

(177) Th. L. W. Bischoff. _Entwicklungsgeschichte des Rehes._ Giessen, 1854.

(178) Th. L. W. Bischoff. "Neue Beobachtungen z. Entwicklungsgesch. des Meerschweinchens." _Abh. d. bayr. Akad._, Cl. II. Vol. X. 1866.

(179) Th. L. W. Bischoff. _Historisch-kritische Bemerkungen z. d. neuesten Mittheilungen üb. d. erste Entwick. d. Säugethiereier._ München, 1877.

(180) M. Coste. _Embryogénie comparée._ Paris, 1837.

(181) E. Haeckel. _Anthropogenie, Entwicklungsgeschichte des Menschen._ Leipzig, 1874.

(182) V. Hensen. "Beobachtungen üb. d. Befrucht. u. Entwick. d. Kaninchens u. Meerschweinchens." _Zeit. f. Anat. u. Entwick._, Vol. I. 1876.

(183) A. Kölliker. _Entwicklungsgeschichte d. Menschen u. d. höheren Thiere._ Leipzig, 1879.

(184) A. Kölliker. "Die Entwick. d. Keimblätter des Kaninchens." _Zoologischer Anzeiger_, Nos. 61, 62, Vol. III. 1880.

(185) N. Lieberkühn. _Ueber d. Keimblätter d. Säugethiere. Doctor-Jubelfeier d. Herrn H. Nasse._ Marburg, 1879.

(186) N. Lieberkühn. "Z. Lehre von d. Keimblättern d. Säugethiere." _Sitz. d. Gesell. z. Beförd. d. gesam. Naturwiss. Marburg_, No. 3. 1880.

(187) Rauber. "Die erste Entwicklung d. Kaninchens." _Sitzungsber. d. naturfor. Gesell. z. Leipzig._ 1875.

(188) C. B. Reichert. "Entwicklung des Meerschweinchens." _Abh. der. Berl. Akad._ 1862.

(189) E. A. Schäfer. "Description of a Mammalian ovum in an early condition of development." _Proc. Roy. Soc._, No. 168. 1876.

(190) E. A. Schäfer. "A contribution to the history of development of the guinea-pig." _Journal of Anat. and Phys._, Vol. X. and XI. 1876 and 1877.

_Foetal Membranes and Placenta of Mammalia._

(191) John Anderson. _Anatomical and Zoological Researches in Western Yunnan._ London, 1878.

(192) K. E. von Baer. _Untersuchungen über die Gefässverbindung zwischen Mutter und Frucht_, 1828.

(193) C. G. Carus. _Tabulae anatomiam comparativam illustrantes._ 1831, 1840.

(194) H. C. Chapman. "The placenta and generative apparatus of the Elephant." _Journ. Acad. Nat. Sc._, Philadelphia. Vol. VIII. 1880.

(195) C. Creighton. "On the formation of the placenta in the guinea-pig." _Journal of Anat. and Phys._, Vol. XII. 1878.

(196) Ecker. _Icones Physiologicae._ 1852-1859.

(197) G. B. Ercolani. _The utricular glands of the uterus_, etc., translated from the Italian under the direction of H. O. Marcy. Boston, 1880. Contains translations of memoirs published in the _Mem. dell'Accad. d. Scienze d. Bologna_, and additional matter written specially for the translation.

(198) G. B. Ercolani. _Nuove ricerche sulla placenta nei pesci cartilaginosi e nei mammiferi._ Bologna, 1880.

(199) Eschricht. _De organis quae respirationi et nutritioni foetus Mammalium inserviunt._ Hafniae, 1837.

(200) A. H. Garrod and W. Turner. "The gravid uterus and placenta of Hyomoschus aquaticus." _Proc. Zool. Soc._, London, 1878.

(201) P. Harting. _Het ei en de placenta van Halicore Dugong. Inaug. diss._ Utrecht. "On the ovum and placenta of the Dugong." Abstract by Prof. Turner. _Journal of Anat. and Phys._, Vol. XIII.

(202) Th. H. Huxley. _The Elements of Comparative Anatomy._ London, 1864.

(203) A. Kölliker. "Ueber die Placenta der Gattung Tragulus." _Verh. der Würzb. phys.-med. Gesellschaft_, Bd. X.

(204) C. D. Meigs. "On the reproduction of the Opossum (Didelphis Virginiana)." _Amer. Phil. Soc. Trans._, Vol. X. 1853.

(205) H. Milne-Edwards. "Sur la Classification Naturelle." _Ann. Sciences Nat._, Sér. 3, Vol. I. 1844.

(206) Alf. Milne-Edwards. "Recherches sur la famille des Chevrotains." _Ann. des Sciences Nat._, Séries V., Vol. II. 1864.

(207) Alf. Milne-Edwards. "Observations sur quelques points de l'Embryologie des Lemuriens, etc." _Ann. Sci. Nat._, Sér. V., Vol. XV. 1872.

(208) Alf. Milne-Edwards. "Sur la conformation du placenta chez le Tamandua." _Ann. des Sci. Nat._, XV. 1872.

(209) Alf. Milne-Edwards. "Recherches s. l. enveloppes foetales du Tatou à neuf bandes." _Ann. Sci. Nat._, Sér. VI., Vol. VIII. 1878.

(210) R. Owen. "On the generation of Marsupial animals, with a description of the impregnated uterus of the Kangaroo." _Phil. Trans._, 1834.

(211) R. Owen. "Description of the membranes of the uterine foetus of the Kangaroo." _Mag. Nat. Hist._, Vol. I. 1837.

(212) R. Owen. "On the existence of an Allantois in a foetal Kangaroo (Macropus major)." _Zool. Soc. Proc._, V. 1837.

(213) R. Owen. "Description of the foetal membranes and placenta of the Elephant." _Phil. Trans._, 1857.

(214) R. Owen. _On the Anatomy of Vertebrates_, Vol. III. London, 1868.

(215) G. Rolleston. "Placental structure of the Tenrec, etc." _Transactions of the Zoological Society_, Vol. V. 1866.

(216) W. Turner. "Observations on the structure of the human placenta." _Journal of Anat. and Phys._, Vol. VII. 1868.

(217) W. Turner. "On the placentation of the Cetacea." _Trans. Roy. Soc. Edinb._, Vol. XXVI. 1872.

(218) W. Turner. "On the placentation of Sloths (Choloepus Hoffmanni)." _Trans. of R. Society of Edinburgh_, Vol. XXVII. 1875.

(219) W. Turner. "On the placentation of Seals (Halichoerus gryphus)." _Trans. of R. Society of Edinburgh_, Vol. XXVII. 1875.

(220) W. Turner. "On the placentation of the Cape Ant-eater (Orycteropus capensis)." _Journal of Anat. and Phys._, Vol. X. 1876.

(221) W. Turner. _Lectures on the Anatomy of the Placenta._ First Series. Edinburgh, 1876.

(222) W. Turner. "Some general observations on the placenta, with special reference to the theory of Evolution." _Journal of Anat. and Phys._, Vol. XI. 1877.

(223) W. Turner. "On the placentation of the Lemurs." _Phil. Trans._, Vol. 166, p. 2. 1877.

(224) W. Turner. "On the placentation of Apes." _Phil. Trans._, 1878.

(225) W. Turner. "The cotyledonary and diffused placenta of the Mexican deer (Cervus Americanus)." _Journal of Anat. and Phys._, Vol. XIII. 1879.

_Human Embryo._

(226) Fried. Ahlfeld. "Beschreibung eines sehr kleinen menschlichen Eies." _Archiv f. Gynaekologie_, Bd. XIII. 1878.

(227) Herm. Beigel und Ludwig Loewe. "Beschreibung eines menschlichen Eichens aus der zweiten bis dritten Woche der Schwangerschaft." _Archiv f. Gynaekologie_, Bd. XII. 1877.

(228) K. Breus. "Ueber ein menschliches Ei aus der zweiten Woche der Gravidität." _Wiener medicinische Wochenschrift_, 1877.

(229) M. Coste. _Histoire générale et particulière du développement des corps organisés_, 1847-59.

(230) A. Ecker. _Icones Physiologicae._ Leipzig, 1851-1859.

(231) V. Hensen. "Beitrag z. Morphologie d. Körperform u. d. Gehirns d. menschlichen Embryos." _Archiv f. Anat. u. Phys._, 1877.

(232) W. His. _Anatomie menschlicher Embryonen_, Part I. _Embryonen d. ersten Monats._ Leipzig, 1880.

(233) J. Kollmann. "Die menschlichen Eier von 6 MM. Grösse." _Archiv f. Anat. und Phys._, 1879.

(234) W. Krause. "Ueber d. Allantois d. Menschen." _Archiv f. Anat. und Phys._, 1875.

(235) W. Krause. "Ueber zwei frühzeitige menschliche Embryonen." _Zeit. f. wiss. Zool._, Vol. XXXV. 1880.

(236) L. Loewe. "Im Sachen der Eihäute jüngster menschlicher Eier." _Archiv für Gynaekologie_, Bd. XIV. 1879.

(237) C. B. Reichert. "Beschreibung einer frühzeitigen menschlichen Frucht im bläschenförmigen Bildungszustande (sackförmiger Keim von Baer) nebst vergleichenden Untersuchungen über die bläschenförmigen Früchte der Säugethiere und des Menschen." _Abhandlungen der königl. Akad. d. Wiss. zu Berlin_, 1873.

(238) Allen Thomson. "Contributions to the history of the structure of the human ovum and embryo before the third week after conception; with a description of some early ova." _Edinburgh Med. Surg. Journal_, Vol. LII. 1839.

COMPARISON OF THE FORMATION OF THE GERMINAL LAYERS IN THE VERTEBRATA.

(239) F. M. Balfour. "A comparison of the early stages in the development of Vertebrates." _Quart. J. of Micr. Science_, Vol. XV. 1875.

(240) F. M. Balfour. "A monograph on the development of Elasmobranch Fishes." London, 1878.

(241) F. M. Balfour. "On the early development of the Lacertilia together with some observations, etc." _Quart. J. of Micr. Science_, Vol. XIX. 1879.

(242) A. Götte. _Die Entwicklungsgeschichte d. Unke._ Leipzig, 1875.

(243) W. His. "Ueb. d. Bildung d. Haifischembryonen." _Zeit. f. Anat. u. Entwick._, Vol. II. 1877. Cf. also His' papers on Teleostei, Nos. 65 and 66.

(244) A. Kowalevsky. "Entwick. d. Amphioxus lanceolatus." _Mém. Acad. des Sciences St Pétersbourg_, Ser. VII. Tom. XI. 1867.

(245) A. Kowalevsky. "Weitere Studien üb. d. Entwick. d. Amphioxus lanceolatus." _Archiv f. mikr. Anal._, Vol. XIII. 1877.

(246) C. Kupffer. "Die Entstehung d. Allantois u. d. Gastrula d. Wirbelthiere." _Zool. Anzeiger_, Vol. II. 1879, pp. 520, 593, 612.

(247) R. Remak. _Untersuchungen üb. d. Entwicklung d. Wirbelthiere_, 1850-1858.

(248) A. Rauber. _Primitivstreifen u. Neurula d. Wirbelthiere._ Leipzig, 1877.

PHYLOGENY OF THE CHORDATA.

(249) F. M. Balfour. _A Monograph on the development of Elasmobranch Fishes_, London, 1878.

(250) A. Dohrn. _Der Ursprung d. Wirbelthiere und d. Princip. d. Functionswechsel._ Leipzig, 1875.

(251) E. Haeckel. _Schöpfungsgeschichte._ Leipzig. _Vide_ also Translation. _The History of Creation._ King and Co., London. 1876.

(252) E. Haeckel. _Anthropogenie._ Leipzig. _Vide_ also Translation. _Anthropogeny._ Kegan Paul and Co., London, 1878.

(253) A. Kowalevsky. "Entwicklungsgeschichte d. Amphioxus lanceolatus." _Mém. Acad. d. Scien. St Pétersbourg_, Ser. VII. Tom. XI. 1867, and _Archiv f. mikr. Anat._, Vol. XIII. 1877.

(254) A. Kowalevsky. "Weitere Stud. üb. d. Entwick. d. einfachen Ascidien." _Archiv f. mikr. Anat._, Vol. VII. 1871.

(255) C. Semper. "Die Stammesverwandschaft d. Wirbelthiere u. Wirbellosen." _Arbeit. a. d. zool.-zoot. Instit. Würzburg_, Vol. II. 1875.

(256) C. Semper. "Die Verwandschaftbeziehungen d. gegliederten Thiere." _Arbeit. a. d. zool.-zoot. Instit. Würzburg_, Vol. III. 1876-1877.

GENERAL WORKS ON EMBRYOLOGY.

(257) Allen Thomson. _British Association Address_, 1877.

(258) A. Agassiz. "Embryology of the Ctenophoræ." _Mem. Amer. Acad. of Arts and Sciences_, Vol. X. 1874.

(259) K. E. von Baer. _Ueb. Entwicklungsgeschichte d. Thiere._ Königsberg, 1828-1837.

(260) F. M. Balfour. "A Comparison of the Early Stages in the Development of Vertebrates." _Quart. Journ. of Micr. Sci._, Vol. XV. 1875.

(261) C. Claus. _Die Typenlehre u. E. Haeckel's sg. Gastræa-theorie._ Wien, 1874.

(262) C. Claus. _Grundzüge d. Zoologie._ Marburg und Leipzig, 1879.

(263) A. Dohrn. _Der Ursprung d. Wirbelthiere u. d. Princip des Functionswechsels._ Leipzig, 1875.

(264) C. Gegenbaur. _Grundriss d. vergleichenden Anatomie._ Leipzig, 1878. _Vide_ also Translation. _Elements of Comparative Anatomy._ Macmillan & Co. 1878.

(265) A. Götte. _Entwicklungsgeschichte d. Unke._ Leipzig, 1874.

(266) E. Haeckel. _Studien z. Gastræa-theorie_, Jena, 1897; and also _Jenaische Zeitschrift_, Vols. VIII. and IX. 1874-5.

(267) E. Haeckel. _Schöpfungsgeschichte._ Leipzig. _Vide_ also Translation, _The History of Creation_. King & Co., London, 1878.

(268) E. Haeckel. _Anthropogenie._ Leipzig. _Vide_ also Translation, _Anthropogeny_. Kegan Paul & Co., London, 1878.

(269) B. Hatschek. "Studien üb. Entwicklungsgeschichte d. Anneliden." _Arbeit. a. d. zool. Instit. d. Univer. Wien._ 1878.

(270) O. and R. Hertwig. "Die Actinien." _Jenaische Zeitschrift_, Vols. XIII. and XIV. 1879.

(271) O. and R. Hertwig. _Die Coelomtheorie._ Jena, 1881.

(272) O. Hertwig. _Die Chætognathen._ Jena, 1880.

(273) R. Hertwig. _Ueb. d. Bau d. Ctenophoren._ Jena, 1880.

(274) T. H. Huxley. _The Anatomy of Invertebrated Animals._ Churchill, 1877.

(274*) T. H. Huxley. "On the Classification of the Animal Kingdom." _Quart. J. of Micr. Science_, Vol. XV. 1875.

(275) N. Kleinenberg. _Hydra, eine anatomisch-entwicklungsgeschichte Untersuchung._ Leipzig, 1872.

(276) A. Kölliker. _Entwicklungsgeschichte d. Menschen u. d. höh. Thiere._ Leipzig, 1879.

(277) A. Kowalevsky. "Embryologische Studien an Würmern u. Arthropoden." _Mém. Acad. Pétersbourg_, Series VII. Vol. XVI. 1871.

(278) E. R. Lankester. "On the Germinal Layers of the Embryo as the Basis of the Genealogical Classification of Animals." _Ann. and Mag. of Nat. Hist._ 1873.

(279) E. R. Lankester. "Notes on Embryology and Classification." _Quart. Journ. of Micr. Sci._, Vol. XVII. 1877.

(280) E. Metschnikoff. "Zur Entwicklungsgeschichte d. Kalkschwämme." _Zeit. f. wiss. Zool._, Vol. XXIV. 1874.

(281) E. Metschnikoff. "Spongiologische Studien." _Zeit. f. wiss. Zool._, Vol. XXXII. 1879.

(282) A. S. P. Packard. _Life Histories of Animals, including Man, or Outlines of Comparative Embryology._ Holt and Co., New York, 1876.

(283) C. Rabl. "Ueb. d. Entwick. d. Malermuschel." _Jenaische Zeitsch._, Vol. X. 1876.

(284) C. Rabl. "Ueb. d. Entwicklung. d. Tellerschneke (Planorbis)." _Morph. Jahrbuch_, Vol. V. 1879.

(285) H. Rathke. _Abhandlungen z. Bildung und Entwicklungsgesch. d. Menschen u. d. Thiere._ Leipzig, 1833.

(286) H. Rathke. _Ueber die Bildung u. Entwicklungs. d. Flusskrebses._ Leipzig, 1829.

(287) R. Remak. _Untersuch. üb. d. Entwick. d. Wirbelthiere._ Berlin, 1855.

(288) Salensky. "Bemerkungen üb. Haeckels Gastræa-theorie." _Archiv f. Naturgeschichte_, 1874.

(289) E. Schäfer. "Some Teachings of Development." _Quart. Journ. of Micr. Science_, Vol. XX. 1880.

(290) C. Semper. "Die Verwandtschaftbeziehungen d. gegliederten Thiere." _Arbeiten a. d. zool.-zoot. Instit. Würzburg_, Vol. III. 1876-7.

GENERAL WORKS DEALING WITH THE DEVELOPMENT OF THE ORGANS OF THE CHORDATA.

(291) K. E. von Baer. _Ueber Entwicklungsgeschichte d. Thiere._ Königsberg, 1828-1837.

(292) F. M. Balfour. _A Monograph on the development of Elasmobranch Fishes._ London, 1878.

(293) Th. C. W. Bischoff. _Entwicklungsgesch. d. Säugethiere u. d. Menschen._ Leipzig, 1842.

(294) C. Gegenbaur. _Grundriss d. vergleichenden Anatomie._ Leipzig, 1878. _Vide_ also English translation, _Elements of Comp. Anatomy_. London, 1878.

(295) M. Foster and F. M. Balfour. _The Elements of Embryology._ Part I. London, 1874.

(296) Alex. Götte. _Entwicklungsgeschichte d. Unke._ Leipzig, 1875.

(297) W. His. _Untersuch. üb. d. erste Anlage d. Wirbelthierleibes._ Leipzig, 1868.

(298) A. Kölliker. _Entwicklungsgeschichte d. Menschen u. der höheren Thiere._ Leipzig, 1879.

(299) H. Rathke. _Abhandlungen ü. Bildung und Entwicklungsgeschichte d. Menschen u. d. Thiere._ Leipzig, 1838.

(300) H. Rathke. _Entwicklungs. d. Natter._ Königsberg, 1839.

(301) H. Rathke. _Entwicklungs. d. Wirbelthiere._ Leipzig, 1861.

(302) R. Remak. _Untersuchungen üb. d. Entwicklung d. Wirbelthiere._ Berlin, 1850-1855.

(303) S. L. Schenk. _Lehrbuch d. vergleich. Embryologie d. Wirbelthiere._ Wien, 1874.

EPIDERMIS AND ITS DERIVATIVES.

_General._

(304) T. H. Huxley. "Tegumentary organs." Todd's _Cyclopædia of Anat. and Physiol._

(305) P. Z. Unna. "Histol. u. Entwick. d. Oberhaut." _Archiv f. mikr. Anat._ Vol. XV. 1876. _Vide_ also Kölliker (No. 298).

_Scales of the Pisces._

(306) O. Hertwig. "Ueber Bau u. Entwicklung d. Placoidschuppen u. d. Zähne d. Selachier." _Jenaische Zeitschrift_, Vol. VIII. 1874.

(307) O. Hertwig. "Ueber d. Hautskelet d. Fische." _Morphol. Jahrbuch_, Vol. II. 1876. (Siluroiden u. Acipenseridæ.)

(308) O. Hertwig. "Ueber d. Hautskelet d. Fische (Lepidosteus u. Polypterus)." _Morph. Jahrbuch_, Vol. V. 1879.

_Feathers._

(309) Th. Studer. _Die Entwick. d. Federn._ Inaug. Diss. Bern, 1873.

(310) Th. Studer. "Beiträge z. Entwick. d. Feder." _Zeit. f. wiss. Zool._, Vol. XXX. 1878.

_Sweat-glands._

(311) M. S. Ranvier. "Sur la structure des glandes sudoripares." _Comptes Rendus_, Dec. 29, 1879.

_Mammary glands._

(312) C. Creighton. "On the development of the Mamma and the Mammary function." _Jour. of Anat. and Phys._, Vol. XI. 1877.

(313) C. Gegenbaur. "Bemerkungen üb. d. Milchdrüsen-Papillen d. Säugethiere." _Jenaische Zeit._, Vol. VII. 1873.

(314) M. Huss. "Beitr. z. Entwick. d. Milchdrüsen b. Menschen u. b. Wiederkäuern." _Jenaische Zeit._, Vol. VII. 1873.

(315) C. Langer. "Ueber d. Bau u. d. Entwicklung d. Milchdrüsen." _Denk. d. k. Akad. Wiss. Wien_, Vol. III. 1851.

THE NERVOUS SYSTEM.

_Evolution of the Nervous System._

(316) F. M. Balfour. "Address to the Department of Anat. and Physiol. of the British Association." 1880.

(317) C. Claus. "Studien üb. Polypen u. Quallen d. Adria. I. Acalephen, Discomedusen." _Denk. d. math.-naturwiss. Classe d. k. Akad. Wiss. Wien_, Vol. XXXVIII. 1877.

(318) Th. Eimer. _Zoologische Studien a. Capri. I. Ueber Beroë ovatus. Ein Beitrag z. Anat. d. Rippenquallen._ Leipzig, 1873.

(319) V. Hensen. "Zur Entwicklung d. Nervensystems." _Virchow's Archiv_, Vol. XXX. 1864.

(320) O. and R. Hertwig. _Das Nervensystem u. d. Sinnesorgane d. Medusen._ Leipzig, 1878.

(321) O. and R. Hertwig. "Die Actinien anat. u. histol. mit besond. Berücksichtigung d. Nervenmuskelsystem untersucht." _Jenaische Zeit._, Vol. XIII. 1879.

(322) R. Hertwig. "Ueb. d. Bau d. Ctenophoren." _Jenaische Zeitschrift_, Vol. XIV. 1880.

(323) A. W. Hubrecht. "The Peripheral Nervous System in Palæo- and Schizonemertini, one of the layers of the body-wall." _Quart. J. of Micr. Science_, Vol. XX. 1880.

(324) N. Kleinenberg. _Hydra, eine anatomisch-entwicklungsgeschichtliche Untersuchung._ Leipzig, 1872.

(325) A. Kowalevsky. "Embryologische Studien an Würmern u. Arthropoden." _Mém. Acad. Pétersbourg_, Series VII., Vol. XVI. 1871.

(326) E. A. Schäfer. "Observations on the nervous system of Aurelia aurita." _Phil. Trans._ 1878.

_Nervous System of the Invertebrata._

(327) F. M. Balfour. "Notes on the development of the Araneina." _Quart. J. of Micr. Science_, Vol. XX. 1880.

(328) B. Hatschek. "Beitr. z. Entwicklung d. Lepidopteren." _Jenaische Zeitschrift_, Vol. XI. 1877.

(329) N. Kleinenberg. "The development of the Earthworm, Lumbricus Trapezoides." _Quart. J. of Micr. Science_, Vol. XIX. 1879.

(330) A. Kowalevsky. "Embryologische Studien an Würmern u. Arthropoden." _Mém. Acad. Pétersbourg_, Series VIII., Vol. XVI. 1871.

(331) H. Reichenbach. "Die Embryonalanlage u. erste Entwick. d. Flusskrebses." _Zeit. f. wiss. Zool._, Vol. XXIX. 1877.

_Central Nervous System of the Vertebrata._

(332) C. J. Carus. _Versuch einer Darstellung d. Nervensystems, etc._ Leipzig, 1814.

(333) J. L. Clark. "Researches on the development of the spinal cord in Man, Mammalia and Birds." _Phil. Trans._, 1862.

(334) E. Dursy. "Beiträge zur Entwicklungsgeschichte des Hirnanhanges." _Centralblatt f. d. med. Wissenschaften_, 1868. Nr. 8.

(335) E. Dursy. _Zur Entwicklungsgeschichte des Kopfes des Menschen und der höheren Wirbelthiere._ Tübingen, 1869.

(336) A. Ecker. "Zur Entwicklungsgeschichte der Furchen und Windungen der Grosshirn-Hemisphären im Foetus des Menschen." _Archiv f. Anthropologie_, v. Ecker und Lindenschmidt. Vol. III. 1868.

(337) E. Ehlers. "Die Epiphyse am Gehirn d. Plagiostomen." _Zeit. f. wiss. Zool._ Vol. XXX., suppl. 1878.

(338) P. Flechsig. _Die Leitungsbahnen im Gehirn und Rückenmark des Menschen. Auf Grund entwicklungsgeschichtlicher Untersuchungen._ Leipzig, 1876.

(339) V. Hensen. "Zur Entwicklung des Nervensystems." _Virchow's Archiv_, Bd. XXX. 1864.

(340) L. Löwe. "Beiträge z. Anat. u. z. Entwick. d. Nervensystems d. Säugethiere u. d. Menschen." Berlin, 1880.

(341) L. Löwe. "Beiträge z. vergleich. Morphogenesis d. centralen Nervensystems d. Wirbelthiere." _Mittheil. a. d. embryol. Instit. Wien_, Vol. II. 1880.

(342) A. M. Marshall. "The Morphology of the Vertebrate Olfactory organ." _Quart. J. of Micr. Science_, Vol. XIX. 1879.

(343) V. v. Mihalkovics. _Entwicklungsgeschichte d. Gehirns._ Leipzig, 1877.

(344) W. Müller. "Ueber Entwicklung und Bau der Hypophysis und des Processus infundibuli cerebri." _Jenaische Zeitschrift._ Bd. VI. 1871.

(345) H. Rahl-Rückhard. "Die gegenseitigen Verhältnisse d. Chorda, Hypophysis etc. bei Haifischembryonen, nebst Bemerkungen üb. d. Deutung d. einzelnen Theile d. Fischgehirns." _Morphol. Jahrbuch_, Vol. VI. 1880.

(346) H. Rathke. "Ueber die Entstehung der glandula pituitaria." _Müller's Archiv f. Anat. und Physiol._, Bd. V. 1838.

(347) C. B. Reichert. _Der Bau des menschlichen Gehirns._ Leipzig, 1859 u. 1861.

(348) F. Schmidt. "Beiträge zur Entwicklungsgeschichte des Gehirns." _Zeitschrift f. wiss. Zoologie_, 1862. Bd. XI.

(349) G. Schwalbe. "Beitrag z. Entwick. d. Zwischenhirns." _Sitz. d. Jenaischen Gesell. f. Med. u. Naturwiss._ Jan. 23, 1880.

(350) Fried. Tiedemann. _Anatomie und Bildungsgeschichte des Gehirns im Foetus des Menschen._ Nürnberg, 1816.

_Peripheral Nervous System of the Vertebrata._

(351) F. M. Balfour. "On the development of the spinal nerves in Elasmobranch Fishes." _Philosophical Transactions_, Vol. CLXVI. 1876; _vide_ also, _A monograph on the development of Elasmobranch Fishes_. London, 1878, pp. 191-216.

(352) W. His. "Ueb. d. Anfänge d. peripherischen Nervensystems." _Archiv f. Anat. u. Physiol._, 1879.

(353) A. M. Marshall. "On the early stages of development of the nerves in Birds." _Journal of Anat. and Phys._, Vol. XI. 1877.

(354) A. M. Marshall. "The development of the cranial nerves in the Chick." _Quart. J. of Micr. Science_, Vol. XVIII. 1878.

(355) A. M. Marshall. "The morphology of the vertebrate olfactory organ." _Quart. J. of Micr. Science_, Vol. XIX. 1879.

(356) A. M. Marshall. "On the head-cavities and associated nerves in Elasmobranchs." _Quart. J. of Micr. Science_, Vol. XXI. 1881.

(357) C. Schwalbe. "Das Ganglion oculomotorii." _Jenaische Zeitschrift_, Vol. XIII. 1879.

_Sympathetic Nervous System._

(360) F. M. Balfour. _Monograph on the development of Elasmobranch Fishes._ London, 1878, p. 173.

(361) S. L. Schenk and W. R. Birdsell. "Ueb. d. Lehre von d. Entwicklung d. Ganglien d. Sympatheticus." _Mittheil. a. d. embryologischen Instit. Wien._ Heft III. 1879.

THE EYE.

_Eye of the Mollusca._

(362) N. Bobretzky. "Observations on the development of the Cephalopoda" (Russian). _Nachrichten d. kaiserlichen Gesell. d. Freunde der Naturwiss. Anthropolog. Ethnogr. bei d. Universität Moskau._

(363) H. Grenacher. "Zur Entwicklungsgeschichte d. Cephalopoden." _Zeit. f. wiss. Zool._, Bd. XXIV. 1874.

(364) V. Hensen. "Ueber d. Auge einiger Cephalopoden." _Zeit. f. wiss. Zool._, Vol. XV. 1865.

(365) E. R. Lankester. "Observations on the development of the Cephalopoda." _Quart. J. of Micr. Science_, Vol. XV. 1875.

(366) C. Semper. _Ueber Sehorgane von Typus d. Wirbelthieraugen._ Wiesbaden, 1877.

_Eye of the Arthropoda._

(367) N. Bobretzky. _Development of Astacus and Palaemon._ Kiew, 1873.

(368) A. Dohrn. "Untersuchungen üb. Bau u. Entwicklung d. Arthropoden. Palinurus und Scyllarus." _Zeit. f. wiss. Zool._, Bd. XX. 1870, p. 264 et seq.

(369) E. Claparède. "Morphologie d. zusammengesetzten Auges bei den Arthropoden." _Zeit. f. wiss. Zool._, Bd. X. 1860.

(370) H. Grenacher. _Untersuchungen üb. d. Sehorgane d. Arthropoden._ Göttingen, 1879.

_The Vertebrate Eye._

(371) J. Arnold. _Beiträge zur Entwicklungsgeschichte des Auges._ Heidelberg, 1874.

(372) Babuchin. "Beiträge zur Entwicklungsgeschichte des Auges." _Würzburger naturwissenschaftliche Zeitschrift_, Bd. 8.

(373) L. Kessler. _Zur Entwicklung d. Auges d. Wirbelthiere._ Leipzig, 1877.

(374) N. Lieberkühn. _Ueber das Auge des Wirbelthierembryo._ Cassel, 1872.

(375) N. Lieberkühn. "Beiträge z. Anat. d. embryonalen Auges." _Archiv f. Anat. und Phys._, 1879.

(376) L. Löwe. "Beiträge zur Anatomie des Auges" and "Die Histogenese der Retina." _Archiv f. mikr. Anat._, Vol. XV. 1878.

(377) V. Mihalkowics. "Untersuchungen über den Kamm des Vogelauges." _Archiv f. mikr. Anat._, Vol. IX. 1873.

(378) W. Müller. "Ueber die Stammesentwickelung des Sehorgans der Wirbelthiere." _Festgabe Carl Ludwig._ Leipzig, 1874.

(379) S. L. Schenk. "Zur Entwickelungsgeschichte des Auges der Fische." _Wiener Sitzungsberichte_, Bd. LV. 1867.

_Accessory organs of the Vertebrate Eye._

(380) G. Born. "Die Nasenhöhlen u. d. Thränennasengang d. Amphibien." _Morphologisches Jahrbuch_, Bd. II. 1876.

(381) G. Born. "Die Nasenhöhlen u. d. Thränennasengang d. amnioten Wirbelthiere. I. Lacertilia. II. Aves." _Morphologisches Jahrbuch_, Bd. V. 1879.

_Eye of the Tunicata._

(382) A. Kowalevsky. "Weitere Studien üb. d. Entwicklung d. einfachen Ascidien." _Archiv f. mikr. Anat._, Vol. VII. 1871.

(383) C. Kupffer. "Zur Entwicklung d. einfachen Ascidien." _Archiv f. mikr. Anat._, Vol. VII. 1872.

AUDITORY ORGANS.

_Auditory organs of the Invertebrata._

(384) V. Hensen. "Studien üb. d. Gehörorgan d. Decapoden." _Zeit. f. wiss. Zool._, Vol. XIII. 1863.

(385) O. and R. Hertwig. _Das Nervensystem u. d. Sinnesorgane d. Medusen._ Leipzig, 1878.

_Auditory organs of the Vertebrata._

(386) A. Boettcher. "Bau u. Entwicklung d. Schnecke." _Denkschriften d. kaiserl. Leop. Carol. Akad. d. Wissenschaft._, Vol. XXXV.

(387) C. Hasse. _Die vergleich. Morphologie u. Histologie d. häutigen Gehörorgane d. Wirbelthiere._ Leipzig, 1873.

(388) V. Hensen. "Zur Morphologie d. Schnecke." _Zeit. f. wiss. Zool._, Vol. XIII. 1863.

(389) E. Huschke. "Ueb. d. erste Bildungsgeschichte d. Auges u. Ohres beim bebrüteten Küchlein." _Isis von Oken_, 1831, and Meckel's _Archiv_, Vol. VI.

(390) Reissner. _De Auris internæ formatione. Inaug. Diss._ Dorpat, 1851.

_Accessory parts of Vertebrate Ear._

(391) David Hunt. "A comparative sketch of the development of the ear and eye in the Pig." _Transactions of the International Otological Congress_, 1876.

(392) W. Moldenhauer. "Zur Entwick. d. mittleren u. äusseren Ohres." _Morphol. Jahrbuch_, Vol. III. 1877.

(393) V. Urbantschitsch. "Ueb. d. erste Anlage d. Mittelohres u. d. Trommelfelles." _Mittheil. a. d. embryol. Instit. Wien_, Heft I. 1877.

OLFACTORY ORGAN.

(394) G. Born. "Die Nasenhöhlen u. d. Thränennasengang d. amnioten Wirbelthiere." Parts I. and II. _Morphologisches Jahrbuch_, Bd. V., 1879.

(395) A. Kölliker. "Ueber die Jacobson'schen Organe des Menschen." _Festschrift f. Rienecker_, 1877.

(396) A. M. Marshall. "Morphology of the Vertebrate Olfactory Organ." _Quart. Journ. of Micr. Science_, Vol. XIX., 1879.

SENSE-ORGANS OF THE LATERAL LINE.

(397) F. M. Balfour. _A Monograph on the development of Elasmobranch Fishes_, pp. 141-146. London, 1878.

(398) H. Eisig. "Die Segmentalorgane d. Capitelliden." _Mittheil. a. d. zool. Station zu Neapel_, Vol. I. 1879.

(399) A. Götte. _Entwicklungsgeschichte d. Unke._ Leipzig, 1875.

(400) Fr. Leydig. _Lehrbuch d. Histologie des Menschen u. d. Thiere._ Hamm. 1857.

(401) Fr. Leydig. _Neue Beiträge z. anat. Kenntniss d. Hautdecke u. Hautsinnesorgane d. Fische._ Halle, 1879.

(402) F. E. Schulze. "Ueb. d. Sinnesorgane d. Seitenlinie bei Fischen und Amphibien." _Archiv f. mikr. Anat._, Vol. VI. 1870.

(403) C. Semper. "Das Urogenitalsystem d. Selachier." _Arbeit. a. d. zool.-zoot. Instil. Würzburg_, Vol. II.

(404) B. Solger. "Neue Untersuchungen zur Anat. d. Seitenorgane d. Fische." _Archiv f. mikr. Anat._, Vol. XVII. and XVIII. 1879 and 1880.

ORIGIN OF THE SKELETON.

(405) C. Gegenbaur. "Ueb. primäre u. secundäre Knochenbildung mit besonderer Beziehung auf d. Lehre von dem Primordialcranium." _Jenaische Zeitschrift_, Vol. III. 1867.

(406) O. Hertwig. "Ueber Bau u. Entwicklung d. Placoidschuppen u. d. Zähne d. Selachier." _Jenaische Zeitschrift_, Vol. VIII. 1874.

(407) O. Hertwig. "Ueb. d. Zahnsystem d. Amphibien u. seine Bedeutung f. d. Genese d. Skelets d. Mundhöhle." _Archiv f. mikr. Anat._, Vol. XI. Supplementheft, 1874.

(408) O. Hertwig. "Ueber d. Hautskelet d. Fische." _Morphol. Jahrbuch_, Vol. II. 1876. (Siluroiden u. Acipenseriden.)

(409) O. Hertwig. "Ueber d. Hautskelet d. Fische (Lepidosteus u. Polypterus)." _Morph. Jahrbuch_, Vol. V. 1879.

(410) A. Kölliker. "Allgemeine Betrachtungen üb. die Entstehung d. knöchernen Schädels d. Wirbelthiere." _Berichte v. d. königl. zoot. Anstalt z. Würzburg_, 1849.

(411) Fr. Leydig. "Histologische Bemerkungen üb. d. Polypterus bichir." _Zeit. f. wiss. Zool._, Vol. V. 1858.

(412) H. Müller. "Ueber d. Entwick. d. Knochensubstanz nebst Bemerkungen, etc." _Zeit. f. wiss. Zool._, Vol. IX. 1859.

(413) Williamson. "On the structure and development of the Scales and Bones of Fishes." _Phil. Trans._, 1851.

(414) Vrolik. "Studien üb. d. Verknöcherung u. die Knochen d. Schädels d. Teleostier." _Niederländisches Archiv f. Zoologie_, Vol. I.

NOTOCHORD AND VERTEBRAL COLUMN.

(415) Cartier. "Beiträge zur Entwicklungsgeschichte der Wirbelsäule." _Zeitschrift für wiss. Zool._, Bd. XXV. Suppl. 1875.

(416) C. Gegenbaur. _Untersuchungen zur vergleichenden Anatomie der Wirbelsäule der Amphibien und Reptilien._ Leipzig, 1862.

(417) C. Gegenbaur. "Ueber die Entwickelung der Wirbelsäule des Lepidosteus mit vergleichend anatomischen Bemerkungen." _Jenaische Zeitschrift_, Bd. III. 1863.

(418) C. Gegenbaur. "Ueb. d. Skeletgewebe d. Cyclostomen." _Jenaische Zeitschrift_, Vol. V. 1870.

(419) Al. Götte. "Beiträge zur vergleich. Morphol. des Skeletsystems d. Wirbelthiere." II. "Die Wirbelsäule u. ihre Anhänge." _Archiv f. mikr. Anat._, Vol. XV. 1878 (Cyclostomen, Ganoiden, Plagiostomen, Chimaera), and Vol. XVI. 1879 (Teleostier).

(420) Hasse und Schwarck. "Studien zur vergleichenden Anatomie der Wirbelsäule u. s. w." Hasse, _Anatomische Studien_, 1872.

(421) C. Hasse. _Das natürliche System d. Elasmobranchier auf Grundlage d. Bau. u. d. Entwick. ihrer Wirbelsäule._ Jena, 1879.

(422) A. Kölliker. "Ueber die Beziehungen der Chorda dorsalis zur Bildung der Wirbel der Selachier und einiger anderen Fische." _Verhandlungen der physical. medicin. Gesellschaft in Würzburg_, Bd. X.

(423) A. Kölliker. "Weitere Beobachtungen über die Wirbel der Selachier insbesondere über die Wirbel der Lamnoidei." _Abhandlungen der senkenbergischen naturforschenden Gesellschaft in Frankfurt_, Bd. V.

(424) H. Leboucq. "Recherches s. l. mode de disparition de la corde dorsale chez les vertébrés supérieurs." _Archives de Biologie_, Vol. I. 1880.

(425) Fr. Leydig. _Anatomisch-histologische Untersuchungen über Fische und Reptilien._ Berlin, 1853.

(426) Aug. Müller. "Beobachtungen zur vergleichenden Anatomie der Wirbelsäule." Müller's _Archiv_. 1853.

(427) J. Müller. "Vergleichende Anatomie der Myxinoiden u. der Cyklostomen mit durchbohrtem Gaumen, I. Osteologie und Myologie." _Abhandlungen der königlichen Akademie der Wissenschaften zu Berlin._ 1834.

(428) W. Müller. "Beobachtungen des pathologischen Instituts zu Jena, I. Ueber den Bau der Chorda dorsalis." _Jenaische Zeitschrift_, Bd. VI. 1871.

(429) A. Schneider. _Beiträge z. vergleich. Anat. u. Entwick. d. Wirbelthiere._ Berlin, 1879.

RIBS AND STERNUM.

(430) C. Claus. "Beiträge z. vergleich. Osteol. d. Vertebraten. I. Rippen u. unteres Bogensystem." _Sitz. d. kaiserl. Akad. Wiss. Wien_, Vol. LXXIV. 1876.

(431) A. E. Fick. "Zur Entwicklungsgeschichte d. Rippen und Querfortsätze." _Archiv f. Anat. und Physiol._ 1879.

(432) C. Gegenbaur. "Zur Entwick. d. Wirbelsäule des Lepidosteus mit vergleich. anat. Bemerk." _Jenaische Zeit._, Vol. III. 1867.

(433) A. Götte. "Beiträge z. vergleich. Morphol. d. Skeletsystems d. Wirbelthiere Brustbein u. Schultergürtel." _Archiv f. mikr. Anat._, Vol. XIV. 1877.

(434) C. Hasse u. G. Born. "Bemerkungen üb. d. Morphologie d. Rippen." _Zoologischer Anzeiger_, 1879.

(435) C. K. Hoffmann. "Beiträge z. vergl. Anat. d. Wirbelthiere." _Niederländ. Archiv Zool._, Vol. IV. 1878.

(436) W. K. Parker. "A monograph on the structure and development of the shoulder-girdle and sternum." _Ray Soc._ 1867.

(437) H. Rathke. _Ueb. d. Bau u. d. Entwicklung d. Brustbeins d. Saurier._ 1853.

(438) G. Ruge. "Untersuch. üb. Entwick. am Brustbeine d. Menschen." _Morphol. Jahrbuch._, Vol. VI. 1880.

THE SKULL.

(439) A. Dugès. "Recherches sur l'Ostéologie et la myologie des Batraciens à leur différents âges." Paris, _Mém. savans étrang._ 1835, and _An. Sci. Nat._ Vol. I. 1834.

(440) C. Gegenbaur. _Untersuchungen z. vergleich. Anat. d. Wirbelthiere_, III. Heft. _Das Kopfskelet d. Selachier._ Leipzig, 1872.

(441) Günther. _Beob. üb. die Entwick. d. Gehörorgans._ Leipzig, 1842.

(442) O. Hertwig. "Ueb. d. Zahnsystem d. Amphibien u. seine Bedeutung f. d. Genese d. Skelets d. Mundhöhle." _Archiv f. mikr. Anat._, Vol. XI. 1874, suppl.

(443) T. H. Huxley. "On the theory of the vertebrate skull." _Proc. Royal Soc._, Vol. IX. 1858.

(444) T. H. Huxley. _The Elements of Comparative Anatomy._ London, 1869.

(445) T. H. Huxley. "On the Malleus and Incus." _Proc. Zool. Soc._, 1869.

(446) T. H. Huxley. "On Ceratodus Forsteri." _Proc. Zool. Soc._, 1876.

(447) T. H. Huxley. "The nature of the craniofacial apparatus of Petromyzon." _Journ. of Anat. and Phys._, Vol. X. 1876.

(448) T. H. Huxley. _The Anatomy of Vertebrated Animals._ London, 1871.

(449) W. K. Parker. "On the structure and development of the skull of the Common Fowl (Gallus Domesticus)." _Phil. Trans._, 1869.

(450) W. K. Parker. "On the structure and development of the skull of the Common Frog (Rana temporaria)." _Phil. Trans._, 1871.

(451) W. K. Parker. "On the structure and development of the skull in the Salmon (Salmo salar)." Bakerian Lecture, _Phil. Trans._, 1873.

(452) W. K. Parker. "On the structure and development of the skull in the Pig (Sus scrofa)." _Phil. Trans._, 1874.

(453) W. K. Parker. "On the structure and development of the skull in the Batrachia." Part II. _Phil. Trans._, 1876.

(454) W. K. Parker. "On the structure and development of the skull in the Urodelous Amphibia." Part III. _Phil. Trans._, 1877.

(455) W. K. Parker. "On the structure and development of the skull in the Common Snake (Tropidonotus natrix)." _Phil. Trans._, 1878.

(456) W. K. Parker. "On the structure and development of the skull in Sharks and Skates." _Trans. Zoolog. Soc._, 1878. Vol. X. pt. IV.

(457) W. K. Parker. "On the structure and development of the skull in the Lacertilia." Pt. I. Lacerta agilis, L. viridis and Zootoca vivipara. _Phil. Trans._, 1879.

(458) W. K. Parker. "The development of the Green Turtle." _The Zoology of the Voyage of H.M.S. Challenger._ Vol. I. pt. V.

(459) W. K. Parker. "The structure and development of the skull in the Batrachia." Pt. III. _Phil. Trans._, 1880.

(460) W. K. Parker and G. T. Bettany. _The Morphology of the Skull._ London, 1877.

(460*) H. Rathke. _Entwick. d. Natter._ Königsberg, 1839.

(461) C. B. Reichert. "Ueber die Visceralbogen d. Wirbelthiere." _Müller's Archiv_, 1837.

(462) W. Salensky. "Beiträge z. Entwick. d. knorpeligen Gehörknöchelchen." _Morphol. Jahrbuch_, Vol. VI. 1880.

Vide also Kölliker (No. 298), especially for the human and mammalian skull; Götte (No. 296).

THE PECTORAL GIRDLE.

(463) Bruch. "Ueber die Entwicklung der Clavicula und die Farbe des Blutes." _Zeit. f. wiss. Zool._, IV. 1853.

(464) A. Dugès. "Recherches sur l'ostéologie et la myologie des Batraciens à leurs différents âges." _Mémoires des savants étrang. Académie royale des sciences de l'institut de France_, Vol. VI. 1835.

(465) C. Gegenbaur. _Untersuchungen zur vergleichenden Anatomie der Wirbelthiere_, 2 Heft. _Schultergürtel der Wirbelthiere. Brustflosse der Fische._ Leipzig, 1865.

(466) A. Götte. "Beiträge z. vergleich. Morphol. d. Skeletsystems d. Wirbelthiere, Brustbein u. Schultergürtel." _Archiv f. mikr. Anat._ Vol. XIV. 1877.

(467) C. K. Hoffmann. "Beiträge z. vergleichenden Anatomie d. Wirbelthiere." _Niederländisches Archiv f. Zool._, Vol. V. 1879.

(468) W. K. Parker. "A Monograph on the Structure and Development of the Shoulder-girdle and Sternum in the Vertebrata." _Ray Society_, 1868.

(469) H. Rathke. _Ueber die Entwicklung der Schildkröten._ Braunschweig, 1848.

(470) H. Rathke. _Ueber den Bau und die Entwicklung des Brustbeins der Saurier_, 1853.

(471) A. Sabatier. _Comparaison des ceintures et des membres antérieurs et postérieurs d. la Série d. Vertébrés._ Montpellier, 1880.

(472) Georg 'Swirski. _Untersuch. üb. d. Entwick. d. Schultergürtels u. d. Skelets d. Brustflosse d. Hechts._ Inaug. Diss. Dorpat, 1880.

THE PELVIC GIRDLE.

(473) A. Bunge. _Untersuch. z. Entwick. d. Beckengürtels d. Amphibien, Reptilien u. Vögel. Inaug. Diss._ Dorpat, 1880.

(474) C. Gegenbaur. "Ueber d. Ausschluss des Schambeins von d. Pfanne d. Hüftgelenkes." _Morph. Jahrbuch_, Vol. II. 1876.

(475) Th. H. Huxley. "The characters of the Pelvis in Mammalia, etc." _Proc. of Roy. Soc._, Vol. XXVIII. 1879.

(476) A. Sabatier. _Comparaison des ceintures et des membres antérieurs et postérieurs dans la Série d. Vertébrés._ Montpellier, 1880.

SKELETON OF THE LIMBS.

(477) M. v. Davidoff. "Beiträge z. vergleich. Anat. d. hinteren Gliedmaassen d. Fische I." _Morphol. Jahrbuch_, Vol. V. 1879.

(478) C. Gegenbaur. _Untersuchungen z. vergleich. Anat. d. Wirbelthiere._ Leipzig, 1864-5. Erstes Heft. Carpus u. Tarsus. Zweites Heft. Brustflosse d. Fische.

(479) C. Gegenbaur. "Ueb. d. Skelet d. Gliedmaassen d. Wirbelthiere im Allgemeinen u. d. Hintergliedmaassen d. Selachier insbesondere." _Jenaische Zeitschrift_, Vol. V. 1870.

(480) C. Gegenbaur. "Ueb. d. Archipterygium." _Jenaische Zeitschrift_, Vol. VII. 1873.

(481) C. Gegenbaur. "Zur Morphologie d. Gliedmaassen d. Wirbelthiere." _Morphologisches Jahrbuch_, Vol. II. 1876.

(482) A. Götte. _Ueb. Entwick. u. Regeneration d. Gliedmaassenskelets d. Molche._ Leipzig, 1879.

(483) T. H. Huxley. "On Ceratodus Forsteri, with some observations on the classification of Fishes." _Proc. Zool. Soc._ 1876.

(484) St George Mivart. "On the Fins of Elasmobranchii." _Zoological Trans._, Vol. X.

(485) A. Rosenberg. "Ueb. d. Entwick. d. Extremitäten-Skelets bei einigen d. Reduction ihrer Gliedmaassen charakterisirten Wirbelthiere." _Zeit. f. wiss. Zool._, Vol. XXIII. 1873.

(486) E. Rosenberg. "Ueb. d. Entwick. d. Wirbelsäule u. d. centrale carpi d. Menschen." _Morphologisches Jahrbuch_, Vol. I. 1875.

(487) H. Strasser. "Z. Entwick. d. Extremitätenknorpel bei Salamandern u. Tritonen." _Morphologisches Jahrbuch_, Vol. V. 1879.

(488) G. 'Swirski. _Untersuch. üb. d. Entwick. d. Schultergürtels u. d. Skelets d. Brustflosse d. Hechts._ Inaug. Diss. Dorpat, 1880.

(489) J. K. Thacker. "Median and paired fins. A contribution to the history of the Vertebrate limbs." _Trans. of the Connecticut Acad._, Vol. III. 1877.

(490) J. K. Thacker. "Ventral fins of Ganoids." _Trans. of the Connecticut Acad._, Vol. IV. 1877.

PLEURAL AND PERICARDIAL CAVITIES.

(491) M. Cadiat. "Du développement de la partie céphalothoracique de l'embryon, de la formation du diaphragme, des pleures, du péricarde, du pharynx et de l'oesophage." _Journal de l'Anatomie et de la Physiologie_, Vol. XIV. 1878.

VASCULAR SYSTEM.

_The Heart._

(492) A. C. Bernays. "Entwicklungsgeschichte d. Atrioventricularklappen." _Morphol. Jahrbuch_, Vol. II. 1876.

(493) E. Gasser. "Ueber d. Entstehung d. Herzens beim Hühn." _Archiv f. mikr. Anat._, Vol. XIV.

(494) A. Thomson. "On the development of the vascular system of the foetus of Vertebrated Animals." _Edinb. New Phil. Journal_, Vol. IX. 1830 and 1831.

(495) M. Tonge. "Observations on the development of the semilunar valves of the aorta and pulmonary artery of the heart of the Chick." _Phil. Trans._ CLIX. 1869.

_Vide_ also Von Baer (291), Rathke (300), Hensen (182), Kölliker (298), Götte (296), and Balfour (292).

_The Arterial System._

(496) H. Rathke. "Ueb. d. Entwick. d. Arterien w. bei d. Säugethiere von d. Bogen d. Aorta ausgehen." Müller's _Archiv_, 1843.

(497) H. Rathke. "Untersuchungen üb. d. Aortenwurzeln d. Saurier." _Denkschriften d. k. Akad. Wien_, Vol. XIII. 1857.

_Vide_ also His (No. 232) and general works on Vertebrate Embryology.

_The Venous System._

(498) J. Marshall. "On the development of the great anterior veins." _Phil. Trans._, 1859.

(499) H. Rathke. "Ueb. d. Bildung d. Pfortader u. d. Lebervenen b. Säugethieren." _Meckel's Archiv_, 1830.

(500) H. Rathke. "Ueb. d. Bau u. d. Entwick. d. Venensystems d. Wirbelthiere." _Bericht. üb. d. naturh. Seminar. d. Univ. Königsberg_, 1838.

_Vide_ also Von Baer (No. 291), Götte (No. 296), Kölliker (No. 298), and Rathke (Nos. 299, 300, and 301).

THE SPLEEN.

(501) W. Müller. "The Spleen." _Stricker's Histology._

(502) Peremeschko. "Ueb. d. Entwick. d. Milz." _Sitz. d. Wien. Akad. Wiss._, Vol. LVI. 1867.

THE SUPRARENAL BODIES.

(503) M. Braun. "Bau u. Entwick. d. Nebennieren bei Reptilien." _Arbeit. a. d. zool.-zoot. Institut Würzburg_, Vol. V. 1879.

(504) A. v. Brunn. "Ein Beitrag z. Kenntniss d. feinern Baues u. d. Entwick. d. Nebennieren." _Archiv f. mikr. Anat._, Vol. VIII. 1872.

(505) Fr. Leydig. _Untersuch. üb. Fische u. Reptilien._ Berlin, 1853.

(506) Fr. Leydig. _Rochen u. Haie._ Leipzig, 1852.

_Vide_ also F. M. Balfour (No. 292), Kölliker (No. 298), Remak (No. 302), etc.

THE MUSCULAR SYSTEM OF THE VERTEBRATA.

(507) G. M. Humphry. "Muscles in Vertebrate Animals." _Journ. of Anat. and Phys._, Vol. VI. 1872.

(508) J. Müller. "Vergleichende Anatomie d. Myxinoiden. Part I. Osteologie u. Myologie." _Akad. Wiss._, Berlin, 1834.

(509) A. M. Marshall. "On the head cavities and associated nerves of Elasmobranchs." _Quart. J. of Micr. Science_, Vol. XXI. 1881.

(510) A. Schneider. "Anat. u. Entwick. d. Muskelsystems d. Wirbelthiere." _Sitz. d. Oberhessischen Gesellschaft_, 1873.

(511) A. Schneider. _Beiträge z. vergleich. Anat. u. Entwick. d. Wirbelthiere._ Berlin, 1879.

_Vide_ also Götte (No. 296), Kölliker (No. 298), Balfour (No. 292), Huxley, etc.

EXCRETORY ORGANS.

_INVERTEBRATA._

(512) H. Eisig. "Die Segmentalorgane d. Capitelliden." _Mitth. a. d. zool. Stat. z. Neapel_, Vol. I. 1879.

(513) J. Fraipont. "Recherches s. l'appareil excréteur des Trematodes et d. Cestoïdes." _Archives de Biologie_, Vol. I. 1880.

(514) B. Hatschek. "Studien üb. Entwick. d. Anneliden." _Arbeit. a. d. zool. Instit. Wien_, Vol. I. 1878.

(515) B. Hatschek. "Ueber Entwick. von Echiurus," etc. _Arbeit. a. d. zool. Instit. Wien_, Vol. III. 1880.

_VERTEBRATA._

_General._

(516) F. M. Balfour. "On the origin and history of the urinogenital organs of Vertebrates." _Journal of Anat. and Phys._, Vol. X. 1876.

(517) Max. Fürbringer[281]. "Zur vergleichenden Anat. u. Entwick. d. Excretionsorgane d. Vertebraten." _Morphol. Jahrbuch_, Vol. IV. 1878.

(518) H. Meckel. _Zur Morphol. d. Harn- u. Geschlechtswerkz. d. Wirbelthiere, etc._ Halle, 1848.

(519) Joh. Müller. _Bildungsgeschichte d. Genitalien_, etc. Düsseldorf, 1830.

(520) H. Rathke. "Beobachtungen u. Betrachtungen ü. d. Entwicklung d. Geschlechtswerkzeuge bei den Wirbelthieren." _N. Schriften d. naturf. Gesell. in Dantzig_, Bd. I. 1825.

(521) C. Semper[281]. "Das Urogenitalsystem d. Plagiostomen u. seine Bedeutung f. d. übrigen Wirbelthiere." _Arb. a. d. zool.-zoot. Instit._ Würzburg, Vol. II. 1875.

(522) W. Waldeyer[281]. _Eierstock u. Ei._ Leipzig, 1870.

_Elasmobranchii._

(523) A. Schultz. "Zur Entwick. d. Selachiereies." _Archiv f. mikr. Anat._, Vol. XI. 1875.

_Vide_ also Semper (No. 521) and Balfour (No. 292).

_Cyclostomata._

(524) J. Müller. "Untersuchungen ü. d. Eingeweide d. Fische." _Abh. d. k. Ak. Wiss._ Berlin, 1845.

(525) W. Müller. "Ueber d. Persistenz d. Urniere b. Myxine glutinosa." _Jenaische Zeitschrift_, Vol. VII. 1873.

(526) W. Müller. "Ueber d. Urogenitalsystem d. Amphioxus u. d. Cyclostomen." _Jenaische Zeitschrift_, Vol. IX. 1875.

(527) A. Schneider. _Beiträge z. vergleich. Anat. u. Entwick. d. Wirbelthiere._ Berlin, 1879.

(528) W. B. Scott. "Beiträge z. Entwick. d. Petromyzonten." _Morphol. Jahrbuch_, Vol. VII. 1881.

_Teleostei._

(529) J. Hyrtl. "Das uropoetische System d. Knochenfische." _Denkschr. d. k. k. Akad. Wiss. Wien_, Vol. II. 1850.

(530) A. Rosenberg. _Untersuchungen üb. die Entwicklung d. Teleostierniere._ Dorpat, 1867.

_Vide_ also Oellacher (No. 72).

_Amphibia._

(531) F. H. Bidder. _Vergleichend-anatomische u. histologische Untersuchungen ü. die männlichen Geschlechts- und Harnwerkzeuge d. nackten Amphibien._ Dorpat, 1846.

(532) C. L. Duvernoy. "Fragments s. les Organes genito-urinaires des Reptiles," etc. _Mém. Acad. Sciences._ Paris. Vol. XI. 1851, pp. 17-95.

(533) M. Fürbringer. _Zur Entwicklung d. Amphibienniere._ Heidelberg, 1877.

(534) F. Leydig. _Anatomie d. Amphibien u. Reptilien._ Berlin, 1853.

(535) F. Leydig. _Lehrbuch d. Histologie._ Hamm, 1857.

(536) F. Meyer. "Anat. d. Urogenitalsystems d. Selachier u. Amphibien." _Sitz. d. naturfor. Gesellsch._ Leipzig, 1875.

(537) J. W. Spengel. "Das Urogenitalsystem d. Amphibien." _Arb. a. d. zool.-zoot. Instit. Würzburg._ Vol. III. 1876.

(538) Von Wittich. "Harn- u. Geschlechtswerkzeuge d. Amphibien." _Zeit. f. wiss. Zool._, Vol. IV.

_Vide_ also Götte (No. 296).

_Amniota._

(539) F. M. Balfour and A. Sedgwick. "On the existence of a head-kidney in the embryo Chick," etc. _Quart. J. of Micr. Science_, Vol. XIX. 1878.

(540) Banks. _On the Wolffian bodies of the foetus and their remains in the adult._ Edinburgh, 1864.

(541) Th. Bornhaupt. _Untersuchungen üb. die Entwicklung d. Urogenitalsystems beim Hühnchen._ Inaug. Diss. Riga, 1867.

(542) Max Braun. "Das Urogenitalsystem d. einheimischen Reptilien." _Arbeiten a. d. zool.-zoot. Instit. Würzburg._ Vol. IV. 1877.

(543) J. Dansky u. J. Kostenitsch. "Ueb. d. Entwick. d. Keimblätter u. d. Wolff'schen Ganges im Hühnerei." _Mém. Acad. Imp. Pétersbourg_, VII. Series Vol. XXVII. 1880.

(544) Th. Egli. _Beiträge zur Anat. und Entwick. d. Geschlechtsorgane._ Inaug. Diss. Zürich, 1876.

(545) E. Gasser. _Beiträge zur Entwicklungsgeschichte d. Allantois, der Müller'schen Gänge u. des Afters._ Frankfurt, 1874.

(546) E. Gasser. "Beob. üb. d. Entstehung d. Wolff'schen Ganges bei Embryonen von Hühnern u. Gänsen." _Arch. für mikr. Anat._, Vol. XIV. 1877.

(547) E. Gasser. "Beiträge z. Entwicklung d. Urogenitalsystems d. Hühnerembryonen." _Sitz. d. Gesell. zur Beförderung d. gesam. Naturwiss._ Marburg, 1879.

(548) C. Kupffer. "Untersuchung über die Entwicklung des Harn- und Geschlechtssystems." _Archiv für mikr. Anat._, Vol. II. 1866.

(549) A. Sedgwick. "Development of the kidney in its relation to the Wolffian body in the Chick." _Quart. J. of Micros. Science_, Vol. XX. 1880.

(550) A. Sedgwick. "On the development of the structure known as the glomerulus of the head-kidney in the Chick." _Quart. J. of Micros. Science_, Vol. XX. 1880.

(551) A. Sedgwick. "Early development of the Wolffian duct and anterior Wolffian tubules in the Chick; with some remarks on the vertebrate excretory system." _Quart. J. of Micros. Science_, Vol. XXI. 1881.

(552) M. Watson. "The homology of the sexual organs, illustrated by comparative anatomy and pathology." _Journal of Anat. and Phys._, Vol. XIV. 1879.

(553) E. H. Weber. _Zusätze z. Lehre von Baue u. d. Verrichtungen d. Geschlechtsorgane._ Leipzig, 1846.

_Vide_ also Remak (No. 302), Foster and Balfour (No. 295), His (No. 297), Kölliker (No. 298).

GENERATIVE ORGANS.

(554) G. Balbiani. _Leçons s. la génération des Vertébrés._ Paris, 1879.

(555) F. M. Balfour. "On the structure and development of the Vertebrate ovary." _Quart. J. of Micr. Science_, Vol. XVIII.

(556) E. van Beneden. "De la distinction originelle du tecticule et de l'ovaire, etc." _Bull. Ac. roy. belgique_, Vol. XXXVII. 1874.

(557) N. Kleinenberg. "Ueb. d. Entstehung d. Eier b. Eudendrium." _Zeit. f. wiss. Zool._, Vol. XXXV. 1881.

(558) H. Ludwig. "Ueb. d. Eibildung im Theirreiche." _Arbeit. a. d. zool.-zoot. Instit. Würzburg_, Vol. I. 1874.

(559) C. Semper. "Das Urogenitalsystem d. Plagiostomen, etc." _Arbeit. a. d. zool.-zoot. Instit. Würzburg_, Vol. II. 1875.

(560) A. Weismann. "Zur Frage nach dem Ursprung d. Geschlechtszellen bei den Hydroiden." _Zool. Anzeiger_, No. 55, 1880.

_Vide_ also O. and R. Hertwig (No. 271), Kölliker (No. 298), etc.

ALIMENTARY CANAL AND ITS APPENDAGES.

(561) B. Afanassiew. "Ueber Bau u. Entwicklung d. Thymus d. Säugeth." _Archiv f. mikr. Anat._, Bd. XIV. 1877.

(562) Fr. Boll. _Das Princip d. Wachsthums._ Berlin, 1876.

(563) E. Gasser. "Die Entstehung d. Cloakenöffnung bei Hühnerembryonen." _Archiv f. Anat. u. Physiol., Anat. Abth._ 1880.

(564) A. Götte. _Beiträge zur Entwicklungsgeschichte d. Darmkanals im Hühnchen._ 1867.

(565) W. Müller. "Ueber die Entwickelung der Schilddrüse." _Jenaische Zeitschrift_, Vol. VI. 1871.

(566) W. Müller. "Die Hypobranchialrinne d. Tunicaten." _Jenaische Zeitschrift_, Vol. VII. 1872.

(567) S. L. Schenk. "Die Bauchspeicheldrüse d. Embryo." _Anatomischphysiologische Untersuchungen._ 1872.

(568) E. Selenka. "Beitrag zur Entwicklungsgeschichte d. Luftsäcke d. Huhns." _Zeit. f. wiss. Zool._ 1866.

(569) L. Stieda. _Untersuch. üb. d. Entwick. d. Glandula Thymus, Glandula thyroidea, u. Glandula carotica._ Leipzig, 1881.

(570) C. Fr. Wolff. "De formatione intestinorum." _Nov. Comment. Akad. Petrop._ 1766.

(571) A. Wölfler. _Ueb. d. Entwick. u. d. Bau d. Schilddrüse._ Berlin, 1880.

_Vide_ also Kölliker (298), Götte (296), His (232 and 297), Foster and Balfour (295), Balfour (292), Remak (302), Schenk (303), etc.

_Teeth._

(572) T. H. Huxley. "On the enamel and dentine of teeth." _Quart. J. of Micros. Science_, Vol. III. 1855.

(573) R. Owen. _Odontography._ London, 1840-1845.

(574) Ch. S. Tomes. _Manual of dental anatomy, human and comparative._ London, 1876.

(575) Ch. S. Tomes. "On the development of teeth." _Quart. J. of Micros. Science_, Vol. XVI. 1876.

(576) W. Waldeyer. "Structure and development of teeth." _Stricker's Histology._ 1870.

_Vide_ also Kölliker (298), Gegenbaur (294), Hertwig (306), etc.

[281] The papers of Fürbringer, Semper and Waldeyer contain full references to the literature of the Vertebrate excretory organs.

CAMBRIDGE: PRINTED BY C. J. CLAY, M.A. & SON, AT THE UNIVERSITY PRESS.

Transcriber's Notes:

Words in italics are surrounded by underscores, _like this_. Superscripts are preceded with a carat: so^I, so^{II}. Subscripts, all of which are in the caption to Figure 250, are enclosed in double braces: chd{{3}}.

Footnotes were indented, renumbered sequentially, and moved to follow the paragraph in which the related anchor occurs. In the bibliography for Chapter 23, entries (517), (521), and (522) have the same footnote anchor, [267]; in the final bibliography, these appear as duplicate footnote anchors [281].

Illustrations and captions were indented and placed within brackets.

Section headers in Chapter 24 were changed from small caps to italics, for consistency with formatting in the remaining chapters.

Punctuation and hyphenation were standardized; missing letters were added. Where the Greek capital letter Lambda appears, it is spelled out.

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