Part 31

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 38a 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."