Part 15

cl. Cloaca. incl. Cloacal involution. oeep. OEsophageal epithelium. pan. Pancreas. th. Thyroid body.

General.

abp. Abdominal pocket (pore). aur. Auricle. cav. Cardinal vein. cauv. Caudal vein. ly. Lymphoid tissue. mm. Muscles. od. Oviduct. pc. Pericardium. pp. body-cavity. sr. Suprarenal body. u. Ureter. vao. Ventral aorta (anterior continuation of bulbus arteriosus). ven. Ventricle. wd. Wolffian duct.

Figs. 1a, 1b, 1c. Three sections through the cloacal region of an embryo belonging to stage O. 1a is the anterior of the three sections. Zeiss A, ocul. 2. Reduced one-third.

1a shews the cloacal involution at its deepest part abutting on the cloacal section of the alimentary tract.

1b is a section through a point somewhat behind this close to the opening of the Wolffian ducts into the cloaca.

1c shews the opening to the exterior in the posterior part of the cloaca, and also the rudiments of the two abdominal pockets (abp).

Fig. 2. Section through the cloacal region of an embryo belonging to stage P. Zeiss A, ocul. 2.

The figure shews the solid anterior extremity of the cloacal involution.

Fig. 3. Longitudinal vertical section through the thyroid body in a stage between O and P. Zeiss a a, ocul. 1.

The figure shews the solid thyroid body (th) connected in front with throat, and terminating below the bulbus arteriosus.

Fig. 4. Pancreas (pan) and adjoining part of the alimentary tract in longitudinal section, from an embryo between stages L and M. Zeiss A, ocul. 2.

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.