Part 4

Fig. 5. Portion of liver network of stage L. Zeiss C, ocul. 2. The section is intended to illustrate the fact that the tubules or cylinders of which the liver is composed are hollow and not solid. Between the liver tubules are seen blood spaces with distinct walls, and blood corpuscles in their interior.

Fig. 6. Section through part of one of the suprarenal bodies of an adult Scyllium hardened in chromic acid. Zeiss C, ocul. 2. The section shews the columnar cells forming the cortex and the more polygonal cells of the medulla.

Fig. 7. Transverse section through the anterior suprarenal body of an adult Scyllium. Zeiss B, ocul. 2. Reduced one-third. The tissue of the suprarenal body has not been filled in, but only the sympathetic ganglion cells which are seen to be irregularly scattered through the substance of the body. The entrance of the nerve (_n_) is shewn, and indications are given of the distribution of the nerve-fibres.

Fig. 8. Section through the sympathetic ganglion of a Scyllium embryo between stages M and N, shewing the connecting trunk between the suprarenal body and the spinal nerve (_spn_), and the appearance of an indication in the ganglion of a portion more directly connected with the nerve. Zeiss D, ocul. 2.

Fig. 9. Section through one of the anterior sympathetic ganglia of an embryo of stage Q, shewing its division into a true ganglionic portion (_syg_), and a suprarenal body (_sr_). Zeiss C, ocul. 2.

EXPLANATION OF PLATES 20 AND 21. (X. p. 479.)

COMPLETE LIST OF REFERENCE LETTERS.

_amg._ Accessory Malpighian body. _cav._ Cardinal vein. _ge._ Germinal epithelium. _k._ True kidney. _l.c._ Longitudinal canal of the Wolffian body connected with vasa efferentia. _mg._ Malpighian body. _nt._ Network and central canal at the base of the testis. _o._ External aperture of urinal cloaca. _od._ Oviduct or Müllerian duct of the female. _od´._ Müllerian duct of the male. _ou._ Openings of ureters in Wolffian duct in the female (fig. 3). _pmg._ Primary Malpighian body. _px._ Growth from vesicle at the end of a segmental tube to join the collecting tube of the preceding segment. _rst._ Rudimentary segmental tube. _ru._ Ureter commencing to be formed. _sb._ Seminal bladder. _sd._ Segmental duct. _st._ Segmental tube. _sto._ Opening of segmental tube into body-cavity. _sur._ Suprarenal body. _t._ Testis. _u._ Ureters. _ve._ Vas efferens. _wb._ Wolffian body. _wd._ Wolffian duct.

PLATE 20.

Fig. 1. Diagrammatic representation of excretory organs on one side of a male Scyllium canicula, natural size.

Fig. 2. Diagrammatic representation of the kidney proper on one side of a female Scyllium canicula, natural size, shewing the ducts of the kidney and the dilated portion of the Wolffian duct.

Fig. 3. Opening of the ureters into the Wolffian duct of a female Scyllium canicula. The figure represents the Wolffian ducts (_wd_) with ventral portion removed so as to expose their inner surface, and shews the junction of the two W. ducts to form the common urinal cloaca, the single external opening of this (_o_), and openings of ureters into one Wolffian duct (_ou_).

Fig. 4. Anterior extremity of Wolffian body of a young male Scyllium canicula shewing the vasa efferentia and their connection with the kidneys and the testis. The vasa efferentia and longitudinal canal are coloured to render them distinct. They are intended to be continuous with the uncoloured coils of the Wolffian body, though this connection has not been very successfully rendered by the artist.

Fig. 5. Part of the Wolffian body of a nearly ripe male embryo of Scyllium canicula as a transparent object. Zeiss a a, ocul. 3. The figure shews two segmental tubes opening into the body-cavity and connected with a primary Malpighian body, and also, by a fibrous connection, with a secondary Malpighian body of the preceding segment. It also shews one segmental tube (_rst_) imperfectly connected with the accessory Malpighian body of the preceding segment of the kidney. The coils of the kidney are represented somewhat diagrammatically.

Fig. 6. Vasa efferentia of a male embryo of Scyllium canicula eight centimetres in length. Zeiss a a, ocul. 2.

There are seen to be at the least six and possibly seven distinct vasa going to as many segments of the Wolffian body and connected with a longitudinal canal in the base of the testis. They were probably also connected with a longitudinal canal in the Wolffian body, but this could not be clearly made out.

Fig. 7. The anterior four vasa efferentia of a nearly ripe embryo. Connected with the foremost one is seen a body which looks like the remnant of a segmental tube and its opening (_rst?_).

Fig. 8. Testis and anterior part of Wolffian body of an embryo of Squatina vulgaris.

The figure is intended to illustrate the arrangement of the vasa efferentia. There are five of these connected with a longitudinal canal in the base of the testis, and with another longitudinal canal in the Wolffian body. From the second longitudinal canal there pass off four ducts to as many Malpighian bodies. Through the Malpighian bodies these ducts are continuous with the several coils of the Wolffian body, and so eventually with the Wolffian duct. Close to the hindermost vas efferens is seen a body which resembles a rudimentary segmental tube (_rst?_).

PLATE 21.

Figs. 1A, 1B, 1C, 1D. Four sections from a female Scyllium canicula of a stage between M and N through the part where the segmental duct becomes split into Wolffian duct and oviduct. Zeiss B, ocul. 2. 1A is the foremost section.

The sections shew that the oviduct arises as a thickening on the under surface of the segmental duct into which at the utmost a very narrow prolongation of the lumen of the segmental duct is carried. The small size of the lumen of the Wolffian duct in the foremost section is due to the section passing through nearly its anterior blind extremity.

Fig. 2. Section close to the junction of the Wolffian duct and oviduct in a female embryo of Scyllium canicula belonging to stage N. Zeiss B, ocul. 2.

The section represented shews that in some instances the formation of the oviduct and Wolffian duct is accompanied by a division of the lumen of the segmental duct into two not very unequal parts.

Figs. 3A, 3B, 3C. Three sections illustrating the formation of a ureter in a female embryo belonging to stage N. Zeiss B, ocul. 2.

3A is the foremost section.

The figures shew that the lumen of the developing ureter is enclosed in front by an independent wall (fig. 3A), but that further back the lumen is partly shut in by the subjacent Wolffian duct, while behind no lumen is present, but the ureter ends as a solid knob of cells without an opening into the Wolffian duct.

Fig. 4. Section through the ureters of the same embryo as fig. 3, but nearer the cloaca. Zeiss B, ocul. 2.

The figure shews the appearance of a transverse section through the wall of cells above the Wolffian duct formed by the overlapping ureters, the lumens of which appear as perforations in it. It should be compared with fig. 9A, which represents a longitudinal section through a similar wall of cells.

Fig. 5. Section through the ureters, the Wolffian duct and the oviduct of a female embryo of Scy. canicula belonging to stage P. Zeiss B, ocul. 2.

Fig. 6. Section of part of the Wolffian body of a male embryo of Scyllium canicula belonging to stage O. Zeiss B, ocul. 2.

The section illustrates (1) the formation of a Malpighian body (_mg_) from the dilatation at the end of a segmental tube, (2) the appearance of the rudiment of the Müllerian duct in the male (_od´_).

Figs. 7_a_, 7_b_. Two longitudinal and vertical sections through part of the kidney of an embryo between stages L and M. Zeiss B, ocul. 2.

7_a_ illustrates the parts of a single segment of the Wolffian body at this stage, vide p. 491. The segmental tube and opening are not in the plane of the section, but the dilated vesicle is shewn into which the segmental tube opens.

7_b_ is taken from the region of the kidney proper. To the right is seen the opening of a segmental tube into the body-cavity, and in the segment to the left the commencing formation of a ureter, vide p. 502.

Fig. 8. Longitudinal and vertical section through the posterior part of the kidney proper of an embryo of Scyllium canicula at a stage between N and O. Zeiss A, ocul. 2.

The section shews the nearly completed ureters, developing Malpighian bodies, &c.

Fig. 9. Longitudinal and vertical section through the anterior part of the kidney proper of the same embryo as fig. 8. Zeiss A, ocul. 2.

The figure illustrates the mode of growth of the developing ureters.

9A. More highly magnified portion of the same section as fig. 9.

Compare with transverse section fig. 4.

Fig. 10. Longitudinal and vertical section through part of the Wolffian body of an embryo of Scyllium canicula at a stage between O and P.

The section contains two examples of the budding out of the vesicle of a segmental tube to form a Malpighian body in its own segment and to unite with the tubulus of the preceding segment close to its opening into the Wolffian duct.

EXPLANATION OF PLATES 22 AND 23[3]. (VIII. p. 168.)

Footnote 3: The figures on these Plates give a fair general idea of the appearance presented by the developing spinal nerves; but the finer details of the original drawings have in several cases become lost in the process of copying.

The figures which are tinted represent sections of embryos hardened in osmic acid; those without colour sections of embryos hardened in chromic acid.

PLATE 22.

Fig. A. Section through the dorsal region of an embryo of _Scyllium stellare_, with the rudiments of two visceral clefts. The section illustrates the general features at a period anterior to the appearance of the posterior nerve-roots.

_nc._ neural canal. _mp._ muscle-plate. _ch._ notochord. _x._ subnotochordal rod. _ao._ rudiment of dorsal aorta. _so._ somatopleure. _sp._ splanchnopleure. _al._ alimentary tract. All the parts of the section except the spinal cord are drawn somewhat diagrammatically.

Figs. B I, B II, B III. Three sections of a _Pristiurus_-embryo. B I is through the heart, B II through the anterior part of the dorsal region, and B III through a point slightly behind this. Drawn with a camera. (Zeiss CC, ocul. 2.)

In B III there is visible a slight proliferation of cells from the dorsal summit of the neural canal.

In B II this proliferation definitely constitutes two club-shaped masses of cells (_pr_), both attached to the dorsal summit of the neural canal. The masses are the rudiments of the posterior nerve-roots.

In B I the rudiments of the posterior roots are of considerable length.

_pr._ rudiment of posterior roots. _nc._ neural canal. _mp._ muscle-plate. _ch._ notochord. _x._ subnotochordal rod. _ao._ dorsal aorta. _so._ somatopleure. _sp._ splanchnopleure. _al._ alimentary canal. _ht._ heart.

Fig. C. Section from a _Pristiurus_-embryo, slightly older than B. Camera. (Zeiss CC, ocul. 2.) The embryo from which this figure was taken was slightly distorted in the process of removal from the blastoderm.

_vr._ rudiment of vertebral body. Other reference letters as in previous figures.

Fig. D a. Section through the dorsal region of a _Torpedo_-embryo with three visceral clefts. (Zeiss CC, ocul. 2.) The section shews the formation of the dorsal nerve-rudiments (_pr_) and of a ventral anterior nerve-rudiment (_ar_), which at this early stage is not distinctly cellular.

_ar._ rudiment of an anterior nerve-root. _y._ cells left behind on the separation of the external skin from the spinal cord. _c._ connective-tissue cells springing from the summit of the muscle-plates. Other reference letters as above.

Fig. D b. Section from dorsal region of a _Torpedo_-embryo somewhat older than D a. Camera. (Zeiss CC, ocul. 2.) The posterior nerve-rudiment is considerably longer than in fig. D a, and its pedicle of attachment to the spinal cord is thinner. The anterior nerve-rudiment, of which only the edge is present in the section, is distinctly cellular.

_m._ mesoblast growing up from vertebral rudiment. _sd._ segmental duct.

Fig. D c. Section from a still older _Torpedo_-embryo. Camera. (Zeiss CC, ocul. 2.) The connective-tissue cells are omitted. The rudiment of the ganglion (_g_) on the posterior root has appeared. The rudiment of the posterior nerve is much longer than before, and its junction with the spinal cord is difficult to detect. The anterior root is now an elongated cellular structure.

_g._ ganglion.

Fig. D d. Longitudinal and vertical section through a _Torpedo_-embryo of the same age as D c.

The section shews the commissures (_x_) uniting the posterior roots.

Fig. E a. Section of a _Pristiurus_-embryo belonging to the second stage. Camera. (Zeiss CC, ocul. 2.) The section shews the constriction of the pedicle which attaches the posterior nerve-rudiments to the spinal cord.

_pr._ rudiment of posterior nerve-root. _nc._ neural canal. _mp._ muscle-plate. _vr._ vertebral rudiment. _sd._ segmental duct. _ch._ notochord. _so._ somatopleure. _sp._ splanchnopleure. _ao._ aorta. _al._ alimentary canal.

Fig. E b. Section of a _Pristiurus_-embryo slightly older than E a. Camera. (Zeiss CC, ocul. 2.) The section shews the formation of the anterior nerve-root (_ar_).

_ar._ rudiment of the anterior nerve-root.

Fig. F. Section of a _Pristiurus_-embryo with the rudiments of five visceral clefts. Camera. (Zeiss CC, ocul. 2.)

The rudiment of the posterior root is seen surrounded by connective-tissue, from which it cannot easily be distinguished. The artist has not been very successful in rendering this figure.

Figs. G 1, G 2, G 3. Three longitudinal and horizontal sections of an embryo somewhat older than F. The embryo from which these sections were taken was hardened 035.png in osmic acid, but the sections have been represented without tinting. G I is most dorsal of the three sections. Camera. (Zeiss CC, ocul. 1.)

_nc._ neural canal. _sp.c._ spinal cord. _pr._ rudiment of posterior root. _ar._ rudiment of anterior root. _mp._ muscle-plate. _c._ connective-tissue cells. _ch._ notochord.

PLATE 23.

Fig. H I. Section through the dorsal region of a _Pristiurus_-embryo in which the rudimentary external gills are present as very small knobs. Camera. (Zeiss CC, ocul. 2.)

The section shews the commencing differentiation of the posterior nerve-rudiment into root (_pr_), ganglion (_sp.g_), and nerve (_n_), and also the attachment of the nerve-root to the spinal cord (_x_). The variations in the size and shape of the cells in the different parts of the nerve-rudiment are completely lost in the figure.

_pr._ posterior nerve-root. _sp.g._ ganglion of posterior root. _n._ nerve of posterior root. _x._ attachment of posterior root to spinal cord. _w._ white matter of spinal cord. _i._ mesoblastic investment to the spinal cord.

Fig. H II. Section through the same embryo as H I. (Zeiss CC, ocul. 1.)

The section contains an anterior root, which takes its origin at a point opposite the interval between two posterior roots.

The white matter has not been very satisfactorily represented by the artist.

Figs. I I, I II. Two sections of a _Pristiurus_-embryo somewhat older than H. Camera. (Zeiss CC, ocul. 1.)

The connective-tissue cells are omitted.

Figs. I a, I b, I c. Three isolated cells from the ganglion of one of the posterior roots of the same embryo.

Figs. K I, K II. Two horizontal longitudinal sections through an embryo in which the external gills have just appeared. K I is the most dorsal of the two sections. Camera. (Zeiss CC, ocul. 1.)

The sections shew the relative positions of the anterior and posterior roots at different levels.

_pr._ posterior nerve-rudiment. _ar._ anterior nerve-rudiment. _sp.c._ spinal cord. _n.c._ neural canal. _mp._ muscle-plate. _mp´._ first-formed muscles.

Fig. L. Longitudinal and vertical section through the trunk of a _Scyllium_-embryo after the external gills have attained their full development. Camera. (Zeiss CC, ocul. 1.)

The embryo was hardened in a mixture of chromic acid and osmic acid.

The section shews the commissures which dorsally unite the posterior roots, and also the junction of the anterior and posterior roots. The commissures are unfortunately not represented in the figure with great accuracy; their outlines are in nature perfectly regular, and not, as in the figure, notched at the junctions of the cells composing them. Their cells are apparently more or less completely fused, and certainly not nearly so clearly marked as in the figure. The commissures stain very deeply with the mixture of osmic and chromic acid, and form one of the most conspicuous features in successful longitudinal sections of embryos so hardened. In sections hardened with chromic acid only they cannot be seen with the same facility. 036.png

_sp. c._ spinal cord. _gr._ grey matter. _w._ white matter. _ar._ anterior root. _pr._ posterior root. _x._ commissure uniting the posterior roots.

Figs. M I, M II. Two sections through the head of the same embryo as fig. B. M I, the foremost of the two, passes through the anterior part of the thickening of epiblast, which becomes involuted as the auditory vesicle. It contains the rudiment of the seventh nerve, VII. Camera. (Zeiss CC, ocul. 2.)

VII. rudiment of seventh nerve. _au._ thickening of external epiblast, which becomes involuted as the auditory vesicle. _n.c._ neural canal. _ch._ notochord. _pp._ body-cavity in the head. _so._ somatopleure. _sp._ splanchnopleure. _al._ throat exhibiting an outgrowth to form the first visceral cleft.

EXPLANATION OF PLATES 24, 25, 26. (XII. p. 549.)

PLATE 24.

LIST OF REFERENCE LETTERS.

_dn._ Modified nucleus of primitive ovum. _do._ Permanent ovum in the act of being formed. _dv._ Developing blood-vessels. _dyk._ Developing yolk. _ep._ Non-ovarian epithelium of ovarian ridge. _fe._ Follicular epithelium. _gv._ Germinal vesicle. _lstr._ Lymphatic region of stroma. _n n._ Nests of nuclei of ovarian region. _o._ Permanent ovum. _ovr._ Ovarian portion of ovarian ridge. _po._ Primitive ovum. _ps e._ Pseudo-epithelium of ovarian ridge. _str._ Stroma ingrowths into ovarian epithelium. _v._ Blood-vessel. _vstr._ Vascular region of stroma adjoining ovarian ridge. _vt._ Vitelline membrane. _x._ Modified nucleus. _yk._ Yolk. _zn._ Zona radiata.

Fig. 1. Transverse section of the ovarian ridge of an embryo of _Scy. canicula_, belonging to stage P, shewing the ovarian region with thickened epithelium and numerous primitive ova. Zeiss C, ocul. 2. _Picric acid._

Fig. 2. Transverse section of the ovarian ridge of an embryo of _Scyllium canicula_, considerably older than stage Q. Zeiss C, ocul. 2. _Picric acid._ Several nests, some with distinct ova, and others with the ova fused together, are present in the section (_nn_), and several examples of modified nuclei in still distinct ova are also represented. One of these is marked _x_. The stroma of the ovarian ridge is exceptionally scanty.

Fig. 3. Transverse section through part of the ovarian ridge, including the ovarian region of an almost ripe embryo of _Scyllium canicula_. Zeiss C, ocul. 2. _Picric acid._ Nuclear nests (_n.n._), developing ova (_d.o._), and ova (_o._), with completely formed follicular epithelium, are now present. The ovarian region is still well separated from the subjacent stroma, and does not appear to contain any cells except those of the original germinal epithelium.

Fig. 4. Section through ovarian ridge of the same embryo as fig. 3, to illustrate the relation of the stroma (_str._) and ovarian region. Zeiss _a a_, ocul. 2. _Picric acid._

Fig. 5. Section through the ovarian ridge of an embryo of _Scyllium canicula_, 10 cm. long, in which the ovary was slightly less advanced than in fig. 3. To illustrate the relation of the ovarian epithelium to the subjacent vascular stroma. Zeiss A, ocul. 2. _Osmic acid._ _y._ points to a small separated portion of the germinal epithelium.

Fig. 6. Section through the ovarian ridge of an embryo of _Scyllium canicula_, slightly older than fig. 5. To illustrate the relation of the ovarian epithelium to the subjacent vascular stroma. Zeiss A, ocul. 2. _Osmic acid._

Fig. 7. More highly magnified portion of the same ovary as fig. 6. To illustrate the same points. Zeiss C, ocul. 2. _Osmic acid._

Fig. 8. Section through the ovarian region (close to one extremity, where it is very small) from a young female of _Scy. canicula_. Zeiss C, ocul. 2. _Picric acid._ It shews the vascular ingrowths amongst the original epithelial cells of the ovarian region.

Fig. 9. Section through the ovarian region of the same embryo as fig. 8, at its point of maximum development. Zeiss A, ocul. 2. _Picric acid._

Fig. 10. Section through superficial part of the ovary of an embryo, shewing the pseudo-epithelium; the cells of which are provided with tails prolonged into the general tissue of the ovary. At _f.e._ is seen a surface view of the follicular epithelium of an ovum. Zeiss C, ocul. 2. _Picric acid._

Fig. 11. Section through part of an ovary of _Scyllium canicula_ of stage Q, with three primitive ova, the most superficial one containing a modified nucleus.

Fig. 12. Section through part of an ovary of an example of _Scyllium canicula_, 8 cm. long. The section passes through a nest of ova with modified nuclei, in which the outlines of the individual ova are quite distinct. Zeiss E, ocul. 2. _Picric acid._

Fig. 13. Section through part of ovary of the same embryo as in fig. 5. The section passes through a nest of nuclei, with at the least two developing ova, and also through one already formed permanent ovum. Zeiss E, ocul. 2. _Osmic acid._

Figs. 14, 15, 16, 17, 18 [Figs. 17 and 18 are on Pl. 25]. Sections through parts of the ovary of the same embryo as fig. 3, with nests of nuclei and a permanent ova in the act of formation. Fig. 14 is drawn with Zeiss D D, ocul. 2. Figs. 15, 16, 17, with Zeiss E, ocul. 2. _Picric acid._

PLATE 25.

LIST OF REFERENCE LETTERS.

_do._ Permanent ovum in the act of being formed. _dyk._ Developing yolk. _fe._ Follicular epithelium. _fe´._ Secondary follicular epithelium. _gv._ Germinal vesicle. _nn._ Nests of nuclei of ovarian region. _o._ Permanent ovum. _pse._ Pseudo-epithelium. _str._ Stroma ingrowths into ovarian epithelium. _vt._ Vitelline membrane. _x._ Modified nucleus. _yk._ Yolk (vitellus). _zn._ Zona radiata.

[Figs. 17 and 18. Vide description of Plate 24.]

Fig. 19. Two nuclei from a nest which appear to be in the act of division. From ovary of the same embryo as fig. 3.

Fig. 20. Section through part of an ovary of the same embryo as fig. 6, containing a nest of nuclei. Zeiss F, ocul. 2. _Osmic acid._

Fig. 21. Ovum from the ovary of a half-grown female, containing isolated deeply stained patches of developing yolk granules. Zeiss B, ocul. 2. _Picric acid._

Fig. 22. Section through a small part of the ovum of an immature female of _Scyllium canicula_, to shew the constitution of the yolk, the follicular epithelium, and the egg membranes. Zeiss E, ocul. 2. _Chromic acid._

Fig. 23. Section through part of the periphery of a nearly ripe ovum of _Scy. canicula_. Zeiss C, ocul. 2. It shews the remnant of the vitelline membrane (_v.t._) separating the columnar but delicate cells of the follicular epithelium (_f.e._) from the yolk (_yk._). In the yolk are seen yolk-spherules in a protoplasmic network. The transverse markings in the yolk-spherules have been made oblique by the artist.

Fig. 24. Fully formed ovum containing a second nucleus (_x_), probably about to be employed as pabulum; from the same ovary as fig. 5. The follicular epithelium is much thicker on the side adjoining the stroma than on the upper side of the ovum. Zeiss F, ocul. 2. _Osmic acid._