CHAP. IX DEVELOPMENT 453 



size only are drawn. In A the seminal ^-esicle and sperm-sac are dissected away 

 from the kidneys and displaced outwards, and the ureters inwards. 

 ah. f>. depression into which the abdominal pore opens ; cL cloaca; els. clasper ; 

 cf. ^.elTerent ducts ; ef>. epididymis ; k. kidney ; k' . vestigial anterior portion of 

 the kidney in the female, represented in the male by the epididymis ; Ir. anterior 

 portion of liver; vi.d. vestigial Miillerian duct in the male; (rs. gullet; ov. 

 ovary ; ovd' . its ccelomic aperture ; ovd" . the common aperture of the oviducts 

 into the cloaca ; r. rectum; sh.gl. .shell-gland; sfd. spermiduct ; sp.s. sperm- 

 sac ; s. V. seminal vesicle ; s. v' . its aperture into the urinogenital sinus ; is. 

 spermary ; ?/. ^. .9. urinogenital sinus; 7/r. ureters ; ^cr' . their apertures into the 

 urinogenital smus ; v. s, urinary sinus. 



varying in diameter from 12-14 mm. downwards : in other 

 Vertebrates which produce large eggs, a similar reduction of 

 one ovary may take place (e.g.., Birds). The oviducts {ovd) 

 are paired, and extend along the whole length of the dorsal 

 wall of the coelome, below the kidneys : anteriorly they 

 unite with one another below the gullet and just in front of 

 the liver, where they communicate with the coelome by 

 a common aperture (ovd') ; posteriorly they open together by 

 a single aperture (ovd") into the cloaca, behind the rectum 

 (r). About the anterior third of each oviduct is narrow and 

 thin-walled ; the posterior two-thirds is wide and distensible, 

 and at the junction of the two parts is a yellowish, glandular 

 mass, the shell-gland (sh.gl). 



Development. — Impregnation is internal, and is effected 

 through the agency of the claspers of the male. The eggs, 

 when ripe, break loose from the surface of the ovary into 

 the ccelome, and thence pass, through the common oviducal 

 aperture, into one or other of the oviducts, where fertilization 

 occurs. As it passes into the dilated portion of the oviduct, 

 the oosperm of Scyllium becomes surrounded first by a 

 gelatinous substance, and then by a horny egg-shell or 

 " Mermaid's purse " ^ secreted by the shell-gland, and having 

 the form of a pillow-case produced at each of its four angles 

 into a long, tendril-like process. The eggs are laid among 

 sea-weed, to which they become attached by their tendrils. 

 ' An egg is contained in the oviduct figured (Fig. 118 B). 



