Fig. 28. — Structure and relations of kidneys and ducts in Gnathostomes. 



A, larval condition with a Miillerian duct (Md) as well as a Wolffian 

 duct (Wd). The Bowman's capsules (Be) of the mesonephros communi- 

 cate with the splanchnocoel (sc) through the mesonephric funnels (mf). 

 i, intestine. B, condition in the adult female. The Miillerian duct persists 

 and functions as an oviduct. The eggs freed from the ovary (0) enter the 

 mouth of the oviduct (oM), and go down it, past the oviducal gland (og) 

 where the shell is secreted. The Wolffian duct is purely excretory in function. 

 C, typical condition of the adult male . The Miillerian duct has disappeared 

 except for vestiges of its opening (rM), and the sperm-sac (ss). Sperms pass 

 from the testis (t) through the vasa efferentia (ve) corresponding to meso- 

 nephric funnels, to the Wolffian duct. The latter is not only excretory 

 but also genital in function , and is also called the vas deferens . D , condition 

 of the adult male Scyllium. The Wolffian duct connects as usual with the 

 anterior mesonephric tubules and vasa efferentia, but the more posterior 

 part of the mesonephros (e) is solely excretory in function ; its tubules run 

 into a collecting duct (cd) which has separated off from the Wolffian duct. 

 The base of the latter or vas deferens is thickened to form the vesicula 

 seminalis (vs), and it and the collecting duct open into the sperm-sac. 



