CHAP, x URINOGENITAL ORGANS 469 



side only are drawn. In A the seminal vesicle and sperm-sac are dissected away 

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

 ab. p. depression into which the abdominal pore opens ; cl. cloaca ; ch. clasper ; 

 ef. d, efferent ducts of spermary ; k. kidney ; k'. vestigial middle portion of the 

 kidney ; k" , anterior portion of the kidney in the male, forming the epididymis ; 

 lr. anterior portion of liver ; vz. d. vestigial Miillerian duct in the male ; a>s. 

 gullet ; ov. ovary ; ovd. oviduct ; ovd' '. its ccelomic aperture ; ovd" . the common 

 aperture of the oviducts into the cloaca; r. rectum; sh.gl. shell-gland; spd. 

 spermiduct ; sp. s. sperm-sac ; s. v. seminal vesicle ; j. v' . its aperture into the 

 urinogenital sinus ; ts. spermary ; n. g. s. urinogenital sinus ; ur. ureters ; ur' . 

 their apertures into the urinogenital sinus ; u. s. urinary sinus. 



sinus, the opening of which into the cloaca is situated on 

 a papilla. 



The female Scyllium has a single ovary (B,ov), suspended 

 by a fold of peritoneum. In the adult it is studded all 

 over with rounded ova in different stages of development, 

 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 ccelome, below the kidneys : anteriorly they 

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

 the liver, where they communicate with the ccelome 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 (p. 433). 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 fertilisation 

 occurs. On reaching 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 



