The Anatomy of Chlamydoselachus 437 



for a distance of 70 mm.; in No. I, for about 100 mm.; while in No. II they are united 

 for a distance of 296 mm. In this respect, as in some others already noted, the mesonephroi 

 of specimen No. II are atypical. 



In general, the mesonephroi are thickest at their posterior ends, where each meso' 

 nephros (considered as a separate entity) has a maximum thickness equal to about one- 

 third its width. Anteriorly, the mesonephroi become thinner very gradually. No. IV 

 is exceptional in that the caudal portion of each mesonephros, for a distance of 15 mm. 

 measured from its posterior end, is abruptly thicker than the part immediately in front 

 of it. This caudal portion has a thickness equal to about two-thirds its width. 



Since the mesonephroi are entirely retroperitoneal, they come into actual contact 

 with the peritoneum only by their broad ventral or ventrolateral surfaces. Wherever 

 the mesonephroi are approximated, they lie close to the base of the dorsal mesentery, 

 which extends along the dorsal median Hne for the entire length of the body cavity. 

 The dorsal mesentery gives rise, laterally, to special mesenteries supporting the oviducal 

 organs and the ovaries; ventrally, to a continuous median mesentery supporting the 

 digestive tube excepting the posterior four -fifths of the valvular intestine and the entire 

 rectum. The mesenteries related to the mesonephroi and to the oviducal organs are 

 particularly important, since these mesenteries contain the collecting tubules and the 

 mesonephric ducts. 



In order to investigate the microscopic structure of the mesonephros and the relations 

 of the right and left mesonephroi to each other, transverse serial sections were cut from 

 segments taken at intervals along the length of these organs in all my specimens. In 

 every case the material was found to be in very poor condition for histological study, but 

 mesonephric tubules and glomeruli were readily identified. In the region of union, the 

 two mesonephroi are sometimes connected by renal tissue, but more often by what 

 appears to be lymphoid tissue. 



Since the mesonephroi are seldom, if ever, disturbed when newly-captured specimens 

 are eviscerated by fishermen, it seems strange that there is so Httle recorded concerning 

 them. CoUett (1897) describes the mesonephroi of his large female specimen as follows: 

 "The kidneys were also very long, the right being the longer (length 780 mm.) and rather 

 flat, the left being more cylindrical, and of a length of 770 mm. Posteriorly, both kidneys 

 form a club-shaped, thickened, coalescent portion terminating somewhat abruptly toward 

 the anus. The length of the coalescent portion is 120 mm." The only additional descrip- 

 tion of the ""kidney" of Chlamydoselachus that I have found is that of Hawkes (1907, p. 

 477), virhich reads as follows: 



The kidney in the female [Chlamydoselachus] is thin dorsoventrally and of irregular 

 breadth. It extends from the region of the oviducal gland to the end of the body cavity, 

 gradually widening as it passes backward in a sinuous line. The sinuosity is due to the 

 arrangement of some of the dorsal muscles. Cephalad to the kidney and apparently uncon- 

 nected with it, there is an irregular body (1.5 cm.) which extends somewhat beyond the end 

 of the abdominal cavity. This is probably the head kidney (pronephros?) which in the adult 

 has retained its position in the region to which the coelome extended in the embryo. 



