v. 13 URINOGENITALS OF ELASMOBRANCHS 163 



functionally with a bladder, but it is a mesodermal structure, derived 

 from the main kidney duct, and not strictly comparable to the endo- 

 dermal bladder of tetrapods. The urinary sinus is a small organ and 

 the volume of liquid excreted is small. 



Fie. 103. A. Urinogenital system of the female, B, of the male dogfish. 

 ah.p. abdominal pores; cl. cloaca; cp. claspers of the male; F. rudiment of the oviducal opening 

 in the male; Md. urinary ducts; mtn. hinder (excretory) part of mesonephros; od. oviduct; 

 oe. cut end of oesophagus; of. oviducal funnel; og. oviducal gland; ov. ovary; P.f. pelvic fins; 

 R. rectum; s.s. sperm-sacs; T. testis; up. urinary papilla in the female; ugp. urogenital papilla 

 in the male; vs. urinary sinus; vc. vasa efferentia; vs. vesicula seminalis; WD. Wolffian duct; 

 Wg. Wolffian gland or mesonephros. (After Bourne, from Goodrich, Vertebrata, A. & C. 



Black, Ltd.) 



The genital system is highly specialized to allow internal fertiliza- 

 tion and the production of a few very yolkv and well-protected eggs. 

 There is a single large ovary, from which the eggs are carried by the 

 cilia of the peritoneum to a pair of funnels lying on either side of the 

 liver behind the heart (Fig. 103). These are apparently formed from 

 proncphric funnels and the Mullerian duct (oviduct) separates from 

 the original nephric duct. In the adult it becomes a thick-walled 

 muscular tube, bearing a swelling, the nidamental gland, the upper 

 part of which produces albumen, the lower the horny egg case. 



