Part 6

Fig. 13. Head of a larva about the same age as fig. 12, ventral aspect.

Fig. 14. Side view of a larva about 15 millims. long, five days after hatching.

Fig. 15. Head of a larva 23 millims. in length.

Fig. 16. Tail of a larva 11 centims. in length.

Fig. 17. Transverse section through the egg-membranes of a just-laid ovum.

We are indebted to Professor W. K. Parker for figs. 12, 14 and 15.

PLATE 35.

Figs. 18-22. Transverse sections of embryo on the third day after impregnation.

Fig. 18. Through head, shewing the medullary keel.

Fig. 19. Through anterior part of trunk.

Fig. 20. Through same region as fig. 19, shewing a groove (_x_) in the epiblast, probably artificially formed in the process of hardening.

Fig. 21. Through anterior part of tail region, shewing partial fusion of layers.

Fig. 22. Through posterior part of tail region, shewing more complete fusion of layers than fig. 21.

Figs. 23-25. Transverse sections of an embryo on the fifth day after impregnation.

Fig. 23. Through fore-brain and optic vesicles.

Fig. 24. Through hind-brain and auditory pits.

Fig. 25. Through anterior part of trunk.

Figs. 26-27. Transverse sections of the head of an embryo on the sixth day after impregnation.

Fig. 26. Through fore-brain and optic vesicles.

Fig. 27. Through hind-brain and auditory pits.

PLATE 36.

Figs. 28-29. Transverse sections of the trunk of an embryo on the sixth day after impregnation.

Fig. 28. Through anterior part of trunk (from a slightly older embryo than the other sections of this stage).

Fig. 29. Slightly posterior to fig. 28, shewing formation of segmental duct as a fold of the somatic mesoblast.

Fig. 30. Longitudinal horizontal section of embryo on the sixth day after impregnation, passing through the mesoblastic somites, notochord, and medullary canal.

Figs. 31-34. Transverse sections through an embryo on the seventh day after impregnation.

Fig. 31. Through anterior part of trunk.

Fig. 32. Through the trunk somewhat behind fig. 31.

Fig. 33. Through tail region.

Fig. 34. Further back than fig. 33, shewing constriction of tail from the yolk.

Figs. 35-37. Transverse sections through an embryo on the eighth day after impregnation.

Fig. 35. Through fore-brain and optic vesicles.

Fig. 36. Through hind-brain, shewing closed auditory pits, &c.

Fig. 37. Through anterior part of trunk.

Fig. 38. Section through tail of an embryo on the ninth day after impregnation.

PLATE 37.

Fig. 39. Section through the olfactory involution and part of fore-brain of a larva on the ninth day after impregnation, shewing olfactory nerve.

Fig. 40. Section through the anterior part of the head of the same larva, shewing pituitary involution.

Figs. 41-43. Transverse sections through an embryo on the eleventh day after impregnation.

Fig. 41. Through fore-part of head, shewing the pituitary body still connected with the oral epithelium.

Fig. 42. Slightly further back than fig. 41, shewing the pituitary body constricted off from the oral epithelium.

Fig. 43. Slightly posterior to fig. 42, to shew olfactory involution, eye, and hyomandibular cleft.

Fig. 44. Longitudinal section of the head of an embryo of 15 millims. in length, a few days after hatching, shewing the structure of the brain.

Fig. 45. Longitudinal section of the head of an embryo, about five weeks after hatching, 26 millims. in length, shewing the structure of the brain. In the front part of the brain the section passes slightly to one side of the median line.

Figs. 46 A to 46 G. Transverse sections through the brain of an embryo 25 millims. in length, about a month after hatching.

Fig. 46 A. Through anterior lobes of cerebrum.

Fig. 46 B. Through posterior lobes of cerebrum.

Fig. 46 C. Through thalamencephalon.

Fig. 46 D. Through optic thalami and optic chiasma.

Fig. 46 E. Through optic lobes and infundibulum.

Fig. 46 F. Through optic lobes and cerebellum.

Fig. 46 G. Through optic lobes and cerebellum, slightly in front of fig. 46 F.

PLATE 38.

Figs. 47 A, B, C. Figures of adult brain.

Fig. 47 A. From the side.

Fig. 47 B. From above.

Fig. 47 C. From below.

Fig. 48. Longitudinal vertical section through the eye of an embryo, about a week after hatching, shewing the vascular membrane surrounding the vitreous humour.

Fig. 49. Diagram shewing the arrangement of the vessels in the vascular membrane of the vitreous humour of adult eye.

Fig. 50. Capillaries of the same vascular membrane.

Fig. 51. Transverse section through anterior part of trunk of an embryo on the ninth day after impregnation, shewing the pronephros and pronephric chamber. 049.png

Fig. 52. Transverse section through the region of the stomach of an embryo 15 millims. in length, shortly after hatching, to shew the glomerulus and peritoneal funnel of pronephros.

Fig. 53. Transverse section through posterior part of the body of an embryo, about a month after hatching, shewing the structure of the mesonephros, the spiral valve, &c.

PLATE 39.

Figs. 54, 55, 56, and 57 are a series of transverse sections through the genital ridge and mesonephros of one side from a larva of 11 centims.

Fig. 54. Section of the lymphatic organ which lies in front of the mesonephros.

Fig. 55. Section near the anterior end of the mesonephros, where the genital sack is completely formed.

Fig. 56. Section somewhat further back, shewing the mode of formation of the genital sack.

Fig. 57. Section posterior to the above, the formation of the genital sack not having commenced, and the genital ridge with primitive germinal cells projecting freely into the body-cavity.

Fig. 58A. View of the testis, mesorchium, and duct of the kidney of the left side of an adult male example of _Lepidosteus_, 60 centims. in length, shewing the vasa efferentia and the longitudinal canal at the base of the mesorchium. The kidney ducts have been cut open posteriorly to shew the structure of the interior.

Fig. 58B. Inner aspect of the posterior lobe of the testis from the same example, to shew the vasa efferentia forming a network on the face of the testis.

Figs. 59A and B. Two sections shewing the structure and relations of the efferent ducts of the testis in the same example.

Fig. 59 A. Section through the inner aspect of a portion of the testis and mesorchium, to shew the network of the vasa efferentia (_nve_) becoming continuous with the seminal tubes (_st_). The granular matter nearly filling the vasa efferentia and the seminal tubes represent the spermatozoa.

Fig. 59 B. Section through part of the kidney and its duct and the longitudinal canal (_lc_) at the base of the mesorchium. Canals (_sc_) are seen passing off from the latter, which enter the kidney and join the uriniferous tubuli. Some of the latter (as well as the seminal tubes) are seen to be filled with granular matter, which we believe to be the remains of spermatozoa.

Fig. 60. Diagram of the urinogenital organs of the left side of an adult female example of _Lepidosteus_ 100 centims. in length. This figure shews the oviduct (_od_) continuous with the investment of the ovary, opening at _od´_ into the dilated part of the kidney duct (segmental duct). It also shews the segmental duct and the junction of the latter with its fellow of the right side to form the so-called bladder, this part being represented as cut open. The kidney (_k_) and lymphatic organ (_ly_) in front of it are also shewn.

PLATE 40.

Fig. 61. Transverse section through the developing pancreas (_p_) of a larva 11 millims. in length.

Fig. 62. Longitudinal section through portions of the stomach, liver, and duodenum of an embryo about a month after hatching, to shew the relations of the pancreas (_p_) to the surrounding parts.

Fig. 63. External view of portions of the liver, stomach, duodenum, &c., of a young Fish, 11 centims. in length, to shew the pancreas (_p_).

Fig. 64. Transverse section through the anterior part of the trunk of an embryo, about a month after hatching, shewing the connection of the air-bladder with the throat (_ab´_).

Fig. 65. Transverse section through the same embryo as fig. 64 further back, shewing the posterior part of the air-bladder (_ab_).

Fig. 66. Viscera of an adult female, 100 centims. in length, shewing the alimentary canal with its appended glands in natural position, and the air-bladder with its aperture into the throat (_ab´_). The proximal part of the duodenum and the terminal part of the intestine are represented as cut open, the former to shew the pyloric valve and the apertures of the pyloric cæca and bile duct, and the latter to shew the spiral valve.

This figure was drawn for us by Professor A. C. Haddon.

PLATE 41.

Fig. 67. Transverse section through the tail of an advanced larva, shewing the neural and hæmal processes, the independently developed interneural and interhæmal elements (_is_), and the commencing dermal fin-rays (_df_).

Fig. 68. Side view of the tail of a larva, 21 minims. in length, dissected so as to shew the structure of the skeleton.

Fig. 69. Longitudinal horizontal section through the vertebral column of a larva, 5.5 centims. in length, on the level of the hæmal arches, shewing the intervertebral rings of cartilage continuous with the arches, the vertebral constriction of the notochord, &c.

Figs. 70 and 71. Transverse sections through the vertebral column of a larva of 5.5 centims. The red represents bone, and the blue cartilage.

Fig. 70. Through the vertebral region, shewing the neural and hæmal arches, the notochordal sheath, &c.

Fig. 71. Through the intervertebral region, shewing the intervertebral cartilage.

Figs. 72 and 73. Transverse sections through the trunk of a larva of 5.5 centims. to shew the structure of the ribs and hæmal arches.

Fig. 72. Through the anterior part of the trunk.

Fig. 73. Through the posterior part of the trunk.

PLATE 42.

Figs. 74-76. Transverse sections through the trunk of the same larva as figs. 72 and 73.

Fig. 74. Through the posterior part of the trunk (rather further back than fig. 73).

Fig. 75. Through the anterior part of the tail.

Fig. 76. Rather further back than fig. 75.

Fig. 77. Longitudinal horizontal section through the vertebral column of a larva of 11 centims., passing through the level of the hæmal arches, and shewing the intervertebral constriction of the notochord, the ossification of the cartilage, &c.

Fig. 78. Transverse section through a vertebral region of the vertebral column of a larva 11 centims. in length.

Fig. 79. Transverse section through an intervertebral region of the same larva as fig. 78.

Fig. 80. Side view of two trunk vertebræ of an adult _Lepidosteus_.

Fig. 81. Front view of a trunk vertebra of adult.

In figures 80 and 81 the red does not represent bone as in the other figures, but simply the ligamentum longitudinale superius.

EXPLANATION OF PLATES 43-45. (XXIV. p. 854.)

N.B. The series of sections are in all cases numbered from before backwards.

LIST OF REFERENCE LETTERS.

_a.p._ Area pellucida. _ep._ Epiblast. _ch._ Notochord. _gr._ Germinal wall. _hy._ Hypoblast. _m._ Mesoblast. _o.p._ Area opaca. _pr.g._ Primitive groove. _pvs._ Primitive streak. _yk._ Yolk of germinal wall.

PLATE 43.

SERIES A, 1 and 2. Sections through the blastoderm before the appearance of primitive streak.

1. Section through anterior part of area pellucida in front of embryonic shield. The hypoblast here forms an imperfect layer. The figure represents about half the section. 2. Section through same blastoderm, in the region of the embryonic shield. Between the epiblast and hypoblast are a number of undifferentiated cells. The figure represents considerably more than half the section.

SERIES B, 1, 2 and 3. Sections through a blastoderm with a very young primitive streak.

1. Section through the anterior part of the area pellucida in front of the primitive streak. 2. Section through about the middle of the primitive streak. 3. Section through the posterior part of the primitive streak.

SERIES C, 1 and 2. Sections through a blastoderm with a young primitive streak.

1. Section through the front end of the primitive streak. 2. Section through the primitive streak, somewhat behind 1. Both figures shew very clearly the difference in character between the cells of the epiblastic mesoblast of the primitive streak, and the more granular cells of the mesoblast derived from the hypoblast.

FIG. D. Longitudinal section through the axial line of the primitive streak, and the part of the blastoderm in front of it, of an embryo duck with a well-developed primitive streak.

PLATE 44.

SERIES E, 1, 2, 3 and 4. Sections through blastoderm with a primitive streak, towards the end of the first stage.

1. Section through the anterior part of the area pellucida. 2. Section a little way behind 1 shewing a forward growth of mesoblast from the primitive streak. 3. Section through primitive streak. 4. Section through posterior part of primitive streak, shewing the great widening of primitive streak behind.

SERIES F, 1 and 2. Sections through a blastoderm with primitive groove.

1. Section shewing a deep pit in front of primitive streak, probably an early indication of the neurenteric canal. 2. Section immediately following 1.

FIG. G. Section through blastoderm with well-developed primitive streak, shewing an exceptionally deep slit-like primitive groove.

SERIES H, 1 and 2. Sections through a blastoderm with a fully-developed primitive streak.

1. Section through the anterior part of area pellucida, shewing the cubical granular hypoblast cells in this region. 2. Section slightly behind 1, shewing the primitive hypoblast cells differentiated into stellate cells, which can hardly be resolved in the middle line into hypoblast and mesoblast.

PLATE 45.

SERIES I, 1, 2, 3, 4 and 5. Sections through blastoderm somewhat older than Series H.

1. Section through area pellucida well in front of primitive streak. 2. Section through area pellucida just in front of primitive streak. 3. Section through the front end of primitive streak. 4. Section slightly behind 3. 5. Section slightly behind 4.

SERIES K, 1, 2, 3, 4 and 5. Sections through a blastoderm in which the first traces of notochord and medullary groove have made their appearance. Rather more than half the section is represented in each figure, but the right half is represented in 1 and 3, and the left in 2 and 4.

1. Section through notochord immediately behind the head fold. 2. Section shewing medullary groove a little behind 1. 3. Section just in front of the primitive streak. 4 and 5. Sections through the front end of the primitive streak.

FIG. L. Surface view of blastoderm with a very young primitive streak.

EXPLANATION OF PLATES 46-53[6]. (XXV. p. 871.)

Footnote 6: The explanations of the figures printed within inverted commas are by Professor Balfour, the rest are by the Editors.

COMPLETE LIST OF REFERENCE LETTERS.

A. Anus. _a._ Dorso-lateral horn of white matter in brain. _a.g._ Accessory gland of male (modified accessory leg gland). _at._ Antenna. _at.n._ Antennary nerve. _b._ Ventro-lateral horn of white matter of brain. _b.c._ Body-cavity. _bl._ Blastopore. C. Cutis. _c._ Postero-dorsal lobe of white matter of brain. _c.g._ Supra-oesophageal ganglia. _cl._ Claw. _c.m._ Circular layer of muscles. _co._ Commissures between the ventral nerve-cords. _co.2._ Second commissure between the ventral nerve-cords. _co_{1}. 2. Mass of cells developed on second commissure. _cor._ Cornea. _c.s.d._ Common duct for the two salivary glands. _cu._ Cuticle. _d._ Ventral protuberance of brain. _d.l.m._ Dorsal longitudinal muscle of pharynx. _d.n._ Median dorsal nerve to integument from supra-oesophageal ganglia. _d.o._ Muscular bands passing from the ventro-lateral wall of the pharynx at the region of its opening into the buccal cavity. E. Eye. E. Central lobe of white matter of brain. _e.n._ Nerves passing outwards from the ventral cords. _ep._ Epidermis. _ep.c._ Epidermis cells. F.1, F.2, _&c._ First and second pair of feet, &c. _f._ Small accessory glandular tubes of the male generative apparatus. F._g._ Ganglionic enlargement on ventral nerve-cord, from which a pair of nerves to foot pass off. _f.gl._ Accessory foot-gland. F._n._ Nerves to feet. _g.co._ Commissures between the ventral nerve-cords containing ganglion cells. _g.o._ Generative orifice. H. Heart. _h._ Cells in lateral division of body-cavity. _hy._ Hypoblast. _i.j._ Inner jaw. _j._ Jaw. _j.n._ Nerves to jaws. L. Lips. _l._ Lens. _l.b.c._ Lateral compartment of body-cavity. _le._ Jaw lever (cuticular prolongation of inner jaw lying in a backwardly projecting diverticulum of the buccal cavity). _l.m._ Bands of longitudinal muscles. M. Buccal cavity. M{1}. Median backward diverticulum of mouth or common salivary duct which receives the salivary ducts. _me._ Mesenteron. _mes._ Mesoblastic somite. _m.l._ Muscles of jaw lever. _m.s._ Sheets of muscle passing round the side walls of pharynx to dorsal body-wall. _od._ Oviduct. _oe._ OEsophagus. _oes.co._ OEsophageal commissures. _o.f.g._ Orifice of duct of foot-gland. _o.j._ Outer jaw. _op._ Optic ganglion. _op.n._ Optic nerve. _or.g._ Ganglionic enlargements for oral papillæ. _or.n._ Nerves to oral papillæ. _or.p._ Oral papillæ. _o.s._ Orifice of duct of segmental organ. _ov._ Ovary. P. Pads on ventral side of foot. _p._ Common duct into which the vasa deferentia open. _p.c._ Posterior lobe of brain. _p.d.c._ Posterior commissure passing dorsal to rectum. _p.f._ Internal opening of nephridium into body-cavity. _ph._ Pharynx. _pi._ Pigment in outer ends of epidermic cells. _pi.r._ Retinal pigment. _p.n._ Nerves to feet. _p.p._ Primary papilla. _pr._ Prostate. R. Rectum. _Re._ Retinal rods. R. _m._ Muscle of claw. _s._ Vesicle of nephridium. _s_{1}. Part of 4th or 5th nephridium which corresponds to vesicle of other nephridia. _s.c._1. Region No. 1 of coiled tube of nephridium. _s.c._2. Region No. 2 of ditto. _s.c._3. Region No. 3 of ditto. _s.c._4. Region No. 4 of ditto. _s.d._ Salivary duct. _s.g._ Salivary gland. _sl.d._ Reservoir of slime gland. _sl.g._ Tubules of slime gland. _s.o._1, 2, 3, _&c._ Nephridia of 1st, 2nd, &c., feet. _s.o.f._ Terminal portion of nephridium. _s.p._ Secondary papilla. _st._ Stomach. _st.e._ Epithelium of stomach. _sy._ Sympathetic nerve running in muscles of tongue and pharynx. _sy´_. Origin of pharyngeal sympathetic nerves. T. Tongue. _t._ Teeth on tongue. _te._ Testis. _tr._ Tracheæ. _tr.c._ Cells found along the course of the tracheæ. _tr.o._ Tracheal stigma. _tr.p._ Tracheal pit. _ut._ Uterus. _v.c._ Ventral nerve cord. _v.d._ Vas deferens. _v.g._ Imperfect ganglia of ventral cord.

PLATE 46.

Fig. 1. _Peripatus capensis_, × 4; viewed from the dorsal surface. (From a drawing by Miss Balfour.)

PLATE 47.

Fig. 2. A left leg of _Peripatus capensis_, viewed from the ventral surface; x 30. (From a drawing by Miss Balfour.)

Fig. 3. A right leg of _Peripatus capensis_, viewed from the front side. (From a drawing by Miss Balfour.)

Fig. 4. The last left (17th) leg of a male _Peripatus capensis_, viewed from the ventral side to shew the papilla at the apex of which the accessory gland of the male, or enlarged crural gland, opens to the exterior. (From a drawing by Miss Balfour.) Prof. Balfour left a rough drawing (not reproduced) shewing the papilla, to which is appended the following note. "Figure shewing the accessory genital gland of male, which opens on the last pair of legs by a papilla on the ventral side. The papilla has got a slit-like aperture at its extremity."

Fig. 5. Ventral view of head and oral region of _Peripatus capensis_. (From a drawing by Miss Balfour.)

PLATE 48.

Figs. 6 and 7 are from one drawing.

Fig. 6. _Peripatus capensis_ dissected so as to shew the alimentary canal, slime glands, and salivary glands; x 3. (From a drawing by Miss Balfour.)

Fig. 7. The anterior end of Fig. 6 enlarged; x 6. (From a drawing by Miss Balfour.) The dissection is viewed from the ventral side, and the lips, L., have been cut through in the middle line behind and pulled outwards, so as to expose the jaws, _j._, which have been turned outwards, and the tongue, T., bearing a median row of chitinous teeth, which branches behind into two. The junction of the salivary ducts, _s.d._, and the opening of the median duct so formed into the buccal cavity is also shewn. The muscular pharynx, extending back into the space between the 1st and 2nd pairs of legs, is followed by a short tubular oesophagus. The latter opens into the large stomach with plicated walls, extending almost to the hind end of the animal. The stomach at its point of junction with the rectum presents an S-shaped ventro-dorsal curve.

A. Anus. _at._ Antenna. F.1, F.2. First and second feet. _j._ Jaws. L. Lips. _oe._ OEsophagus. _or.p._ Oral papilla. _ph._ Pharynx. R. Rectum. _s.d._ Salivary duct. _s.g._ Salivary gland. _sl.d._ Slime reservoir. _sl.g._ Portion of tubules of slime gland. _st._ Stomach. T. Tongue in roof of mouth.

Fig. 8. _Peripatus capensis_, x 4; male. (From a drawing by Miss Balfour.) Dissected so as to shew the nervous system, slime glands, ducts of the latter passing into the oral papilla, accessory glands opening on the last pair of legs (enlarged crural glands), and segmental organs, viewed from dorsal surface. The first three pairs of segmental organs consist only of the vesicle and duct leading to the exterior. The fourth and fifth pairs are larger than the succeeding, and open externally to the crural glands. The ventral nerve-cords unite behind dorsal to the rectum.

A. Anus. _a.g._ Accessory generative gland, or enlarged crural gland of the 17th leg. _at._ Antenna. _c.g._ Supra-oesophageal ganglia with eyes. _co._ Commissures between the ventral nerve-cords. _d.n._ Large median nerve to dorsal integument from hinder part of brain. F.1, 2, &c. Feet. _g.o._ Generative orifice. _oe._ OEsophagus. _oes.co._ OEsophageal commissures. _or.p._ Oral papilla. _p.d.c._ Posterior dorsal commissure between the ventral nerve-cords. _ph._ Pharynx. _p.n._ Nerves to feet, one pair from each ganglionic enlargement. _sl.d._ Reservoir of slime gland. _sl.g._ Tubules of slime gland. _s.o._1, 2, 3, _&c._ Segmental organs. _v.c._ Ventral nerve-cords. _v.g._ Imperfect ganglia of ventral cords.

Figs. 9 and 10. Left jaw of _Peripatus capensis_ (male), shewing reserve jaws. (From a drawing by Miss Balfour.)

Fig. 9. Inner jaw.

Fig. 10. Outer jaw.

PLATE 49.

Figs. 11-16. A series of six transverse sections through the head of _Peripatus capensis._

Fig. 11. The section is taken immediately behind the junction of the supra-oesophageal ganglia, _c.g._, and passes through the buccal cavity, M., and jaws, _o.j._ and _i.j._

Fig. 12. The section is taken through the hinder part of the buccal cavity at the level of the opening of the mouth into the pharynx and behind the jaws. The cuticular rod-like continuation (_le._) of the inner jaw lying in a backwardly directed pit of the buccal cavity is shewn; on the right hand side the section passes through the opening of this pit.

Fig. 13. The section passes through the front part of the pharynx, and shews the opening into the latter of the median backward diverticulum of the mouth (M{1}), which receives the salivary ducts. It also shews the commencement of the ventral nerve-cords, and the backwardly projecting lobes of the brain.