Chapter D: I, D II, D III. Diagrammatic longitudinal sections of an animal, (3)

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.

Fig. 14. The section passes through the anterior part of the pharynx at the level of the second commissure (_co._ 2), between the ventral nerve-trunks, and shews the mass of cells developed on this commissure, which is in contact with the epithelium of the backward continuation of the buccal cavity (M{1}).

Fig. 15. Section through the point of junction of the salivary ducts with the median oral diverticulum.

Fig. 16. Section behind the pharynx through the oesophagus.

_b.c._ Body-cavity. C. Cutis. _c.b.c._ Central compartment of body-cavity. _c.g._ Supra-oesophageal ganglia. _c.m._ Layer of circular muscles. _co._ Commissure between ventral nerve-cords. _co._ 2. Second commissure between the ventral nerve-cords. _co{1}._ 2. Mass of cells developed on second commissure (probably sensory). _c.s.d._ Common duct for the two salivary glands. _d.l.m._ Dorsal longitudinal muscles of pharynx. _d.o._ Muscles serving to dilate the opening of the pharynx. _Ep._ Epidermis. _e.n._ Nerve passing outwards from ventral nerve-cord. H. Heart. _i.j._ Inner jaw. _j.p._ Jaw papillæ. _L._ Lips of buccal cavity. _l.b.c._ Lateral compartment of body-cavity. _le._ Rod-like cuticular continuation of inner jaw, lying in a pit of the buccal cavity. _l.m._ Bands of longitudinal muscles. M. Buccal cavity. M{1}. Median backward continuation of buccal cavity. _m.l._ Muscles of jaw lever. _m.s._ Muscular sheets passing from side walls of pharynx to dorsal body-wall. _oe._ OEsophagus. _oes.co._ OEsophageal commissures. _o.j._ Outer jaw. _ph._ Pharynx. _s.d._ Salivary duct. _s.g._ Salivary gland. _sl.d._ Reservoir of slime gland. _sy._ Sympathetic nerves running in muscles of tongue or pharynx. _sy{1}._ Origin of sympathetic nerves to pharynx. T. Tongue. _v.c._ Ventral nerve-cords.

Figs. 17, 18. Two longitudinal horizontal sections through the head of _Peripatus capensis_. Fig. 17 is the most ventral. They are both taken ventral to the cerebral ganglia. In Fig. 17 dorsal tracheal pits are shewn with tracheæ passing off from them. (Zeiss a a, Hartnack's camera.) C. Cutis. _c.s.d._ Common salivary duct. _ep._ Epidermis. _i.j._ Inner jaw. M. Buccal cavity. M{1}. Median backward diverticulum of mouth. _o.j._ Outer jaw. _s.d._ Salivary ducts. T. Tongue. _t._ Teeth on tongue. _tr._ Tracheæ. _tr.p._ Tracheal pits.

PLATE 50.

Fig. 19. "A, B, C, D, E, F, G." Seven transverse sections illustrating the structure of the supra-oesophageal ganglia. (Zeiss A, Hartnack's camera.) _a._ Dorso-lateral horn of white matter. _b._ Ventro-lateral horn of white matter. _c._ Postero-dorsal lobe of white matter. _d._ Ventral protuberance of brain. _e._ Central lobe of white matter. _o.p._ Optic ganglion.

"A. Section through anterior portions of ganglia close to the origin of the antennary nerve. B. Section a little in front of the point where the two ganglia unite. C. Section close to anterior junction of two ganglia. D. Section through origin of optic nerve on the right side. E. Section shewing origin of the optic nerve on the left side. F. Section through the dorso-median lobe of white matter. G. Section near the termination of the dorsal tongue of ganglion cells."

PLATE 51.

Fig. 20. Portion of a transverse section through the hinder part of _Peripatus capensis_ (male). The section passes through a leg, and shews the opening of the segmental organ (_o.s._), and of a crural gland, _o.f.g._, and the forward continuation of the enlarged crural gland of the 17th leg (_f.gl._). (Zeiss a a, Hartnack's camera.) _a.g._ accessory gland of male (modified crural gland of last leg). C. Cutis. _cl._ Claw. _cu._ Cuticle. _ep._ Epidermis. _f.gl._ Crural gland. _h._ Cells in lateral compartment of body-cavity. _o.f.g._ Orifice of accessory foot gland. _o.s._ Opening of segmental organ. P. Three spinous pads on ventral surface of foot. _pr._ Prostate. R.M. Retractor muscle of claw. _s._ Vesicle of nephridium. _s.c.i._ Region No. 1 of coiled part of nephridium. _sl.g._ Tubule of slime gland. _s.o.t._ Terminal portion of nephridium. _st._ Stomach. _st.e._ Epithelium of stomach. _v.c._ Ventral nerve-cord. _v.d._ Vas deferens.

Fig. 21. "Longitudinal vertical section through the supra-oesophageal ganglion and oesophageal commissures of _Peripatus capensis_. (Zeiss a a, Hartnack.)" _at._ Antenna. _e._ Central lobe of white matter. _j._ Part of jaw. _s.g._ Salivary gland.

Fig. 22: drawn by Miss Balfour. Brain and anterior part of the ventral nerve-cords of _Peripatus capensis_ enlarged and viewed from the ventral surface. The paired appendages (_d_) of the ventral surface of the brain are seen, and the pair of sympathetic nerves (_sy_{1}) arising from the ventral surface of the hinder part.

From the commencement of the oesophageal commissures (_oes.co._) pass off on each side a pair of nerves to the jaws (_j.n._).

The three anterior commissures between the ventral nerve-cords are placed close together; immediately behind them the nerve-cords are swollen, to form the ganglionic enlargements from which pass off to the oral papillæ a pair of large nerves on each side (_or.n._).

Behind this the cords present a series of enlargements, one pair for each pair of feet, from which a pair of large nerves pass off on each side to the feet (_p.n_). _at.n._ Antennary nerves. _co._ Commissures between ventral cords. _d._ Ventral appendages of brain. E. Eye. _e.n._ Nerves passing outwards from ventral cord. _F.g._ Ganglionic enlargements from which nerves to feet pass off. _j.n._ Nerves to jaws. _or.g._ Ganglionic enlargement from which nerves to oral papillæ pass off. _or.n._ Nerves to oral papillæ. _p.c._ Posterior lobe of brain. _p.n._ Nerves to feet. _s.y._ Sympathetic nerves.

Fig. 23. "Longitudinal horizontal section through the head of _Peripatus capensis_, shewing the structure of the brain, the antennary and optic nerves, &c. (Zeiss a a, Hartnack's camera.)" _at._ Antenna. _at.n._ Antennary nerve. _cor._ Cornea. _e._ Central mass of white matter. _l._ Lens. _op.n._ Optic nerve. _ph._ Pharynx. _p.p._ Primary papilla covered with secondary papillæ and terminating in a long spine. _sy._ Pharyngeal sympathetic nerves.

Fig. 24. "Eye of _Peripatus capensis_, as shewn in a longitudinal horizontal section through the head. The figure is so far diagrammatic that the lens is represented as filling up the whole space between the rods and the cornea. In the actual section there is a considerable space between the parts, but this space is probably artificial, being in part caused by the shrinkage of the lens and in part by the action of the razor. (Zeiss C, Hartnack's camera.)" (It appears that the ganglionic region of the eye is covered by a thin capsule, which is omitted in the figure.)

_cor._ Cornea. _l._ Lens. _op._ Optic ganglion. _op.n._ Optic nerve. _pi.r._ Pigment. _Re._ rods. _s.p._ Secondary papillæ.

Fig. 25. Longitudinal horizontal section through the dorsal skin, shewing the peculiar arrangement of the circular muscular fibres. (Zeiss A, Hartnack's camera.)

PLATE 52.

Fig. 26. Portion of ventral cord of _Peripatus capensis_ enlarged, shewing two ganglionic enlargements and the origin of the nerves and commissures. (From a drawing by Miss Balfour.)

_co._ Commissures. E._n._ Nerves passing out from ventral cords. F._n._ Nerves to feet. _g.co._ Commissures between the ventral cords containing ganglion cells. _v.g._ Ganglionic enlargements.

Fig. 27. Segmental organ from the 5th pair of legs of _Peripatus capensis_. This nephridium resembles those of the 4th legs, and differs from all the others in its large size and in the absence of any dilatation giving rise to a collecting vesicle on its external portion (enlarged). The terminal portion has the same histological characters as in the case of the hinder segmental organs. (From a drawing by Miss Balfour.)

Fig. 28. Segmental organ or nephridium from the 9th pair of legs of _Peripatus capensis_, shewing the external opening, the vesicle, the coiled portion and the terminal portion with internal opening (enlarged). (From a drawing by Miss Balfour.)

_o.s._ External opening of segmental organ. _p.f._ Internal opening of nephridium into the body-cavity (lateral compartment). _s._ Vesicle of segmental organ. _s_{1}. Portion of segmental organ of 4th and 5th legs, corresponding to vesicle of the other nephridia. _s.c._1. First or external portion of coiled tube of nephridium, lined by columnar epithelium with small nuclei; the cells project for very different distances, giving the inner boundary of this region a ragged appearance. _s.c._2. Region No. 2 of coiled tube of nephridium, lined by small closely-packed columnar cells. _s.c._3. Region No. 3 of coiled tube of segmental organ, lined by large flat cells with large disc-shaped nuclei. _s.c._4. Region No. 4 of coiled tube of nephridium; this region is very short and lined by small columnar cells. _s.o.t._ Terminal portion of nephridium.

Fig. 29. "Portion of nephridium of the hindermost leg of _Peripatus capensis_, seen in longitudinal and vertical section. The figure is given to shew the peritoneal funnel of the nephridium. Portions of the collecting sack (_s._) and other parts are also represented. (Zeiss B, Hartnack's camera.)"

_p.f._ Peritoneal funnel. _s._ Vesicle. _s.c.1_, _s.c.2_, _s.c.3._ Portions of coiled tube.

Fig. 30. "Section through a tracheal pit and diverging bundles of tracheal tubes" taken transversely to the long axis of the body. (Zeiss E, oc. 2.) (From a rough drawing by Prof. Balfour.)

_tr._ _Tracheæ_, shewing rudimentary spiral fibre. _tr.c._ Cells resembling those lining the tracheal pits, which occur at intervals along the course of the tracheæ. _tr.s._ Tracheal stigma. _tr.p._ Tracheal pit.

Fig. 31. "Sense organs and nerves attached from antenna of _Peripatus capensis_ (Zeiss, immersion 2, oc. 2.)" (From a rough drawing by Prof. Balfour.) The figure shews the arrangement of the epidermis cells round the base of the spine. The spine is seen to be continuous with the inner layer of the cuticle.

Fig. 32. Section through the skin of _Peripatus capensis_; it shews the secondary papillæ covered with minute spinous tubercles and the relation of the epidermis to them. (The cuticle in the process of cutting has been torn away from the subjacent cells.) The cells of the epidermis are provided with large oval nuclei, and there is a deposit of pigment in the outer ends of the cells. The granules in the protoplasm of the inner ends of the cells are arranged in lines, so as to give a streaked appearance. (Zeiss E, oc. 2.) (From a rough drawing by Prof. Balfour.)

_c._ Dermis. _cu._ Cuticle. _ep.c._ Epidermis cells. _pi._ Deposit of pigment in outer ends of epidermis cells. _s.p._ Secondary papillæ.

Fig. 33. Female generative organs of _Peripatus capensis_, × 5. (From a rough drawing by Prof. Balfour.) The following note was appended to this drawing: "Ovary rather to dorsal side, lying in a central compartment of body-cavity and attached to one of the longitudinal septa, dividing this from the lateral compartment between the penultimate pair of legs and that next in front. The oviducts cross before opening to the exterior, the right oviduct passing under the rectum and the left over it. They meet by opening into a common vestibule, which in its turn opens below the anus. On each side of it are a pair of short papillæ (aborted feet?)."

F. 16, 17. Last two pairs of legs. _od._ Oviduct. _ov._ Ovary. _ut._ Uterus. _v.c._ Nerve-cord.

PLATE 53.

Figs. 34-39. Five young embryos of _Peripatus capensis_; ventral view. All, excepting Fig. 37, from drawings by Miss Balfour. In figures 34 to 38_a_ denotes what is probably the anterior extremity.

Fig. 34, Stage A. Youngest embryo found, with slightly elongated blastopore.

Fig. 35, Stage B. Embryo with three mesoblastic somites and elongated blastopore. The external boundaries of the somites are not distinct.

Fig. 36, Stage C. Embryo with five somites. The blastopore is closing in its middle portion.

Fig. 37, Stage D. The blastopore has completely closed in its middle portion, and given rise to two openings, the future mouth and anus. (From a rough drawing left by Professor Balfour.) (Zeiss A, Camera Oberhaus. on level of stage.)

The following note was appended to this drawing in his handwriting: "Young larva of _Peripatus capensis_. I could not tell for certain which was the anterior end. Length, 1.34 mm."

Fig. 38, Stage E. Embryo with about thirteen mesoblastic somites in which the flexure of the hind part of the body has commenced. The remains of the original blastopore are present as the mouth, placed between the second pair of mesoblastic somites, and the anus placed on the concavity of the commencing flexure of the hind part of the body.

Fig. 39. Side view of same embryo.

Figs. 40-42. Drawings by Professor Balfour of three transverse sections through the embryo from which fig. 36 was taken. (Zeiss c, Camera.) Figs. 40 and 42 pass through the region of the blastopore.

_bl._ Blastopore. _ep._ Epiblast. _hy._ Hypoblast. _me._ Mesenteron. _mes._ Mesoblastic somite.

Fig. 43. Male generative organs of _Peripatus capensis_, viewed from the dorsal surface. (From a drawing by Miss Balfour.)

_a.g._ Enlarged crural glands of last pair of legs. F.16, 17. Last pairs of legs. _f._ Small accessory glandular tubes. _p._ Common duct into which vasa deferentia open. _p.r._ Prostate. _te._ Testes. _v.c._ Nerve-cord. _v.d._ Vas deferens.

THE CAMBRIDGE SCIENTIFIC INSTRUMENT COMPANY.]

THE CAMBRIDGE SCIENTIFIC INSTRUMENT COMPANY.]

TRANSCRIBER'S NOTES:

Underscores surround text in italics, _like this_. Raised dots in numbers were converted to decimals. Superscript letters are enclosed in braces, e.g. P{1}.

Use of periods and commas in the abbreviations within and referring to illustrations is inconsistent. Often punctuation marks do not match the illustrations to which they refer. Periods were retained; commas were added to separate figure numbers from abbreviations within the figure. Spacing within the abbreviations was standardized. Occasionally, identification marks referenced in the text do not match the illustration (for example, discussion of Figure 10, Plate 2, where epiblast is identified with _e_ in the text, but with E in the illustration).

Footnotes were renumbered sequentially, indented, and moved to follow the paragraph or section in which the anchor occurs.

Other changes:

Footnote 4: 're-agent' to 'reagent'
Explanation of Plates, Plate 35, Figures 26-27: 'Tranverse' to 'Transverse'