GENITAL DUCTS 91 



the mesonephric tubules with the other (the mesonephric or 

 Wolffian duct). Meanwhile the pronephric funnels fuse to a single 

 opening (ostium abdominale), which shifts backwards to open at the 

 anterior end of the abdominal coelom (p. 132). In the male the 

 Miillerian duct undergoes more or less complete degeneration, 

 especially in its middle region. On the contrary in the female, 

 the Miillerian duct enlarges into the oviduct of the adult. From 

 this it was concluded that the pronephric duct became modified 

 into the oviduct. 



In the Amniota, however, no such intimate connection between 

 the developing oviduct and the pronephros can be traced. As a rule, 

 the duct arises in front from a groove or outgrowth of the coelomic 

 epithelium, along the mesonephric ridge, which then grows freely 

 backwards to open into the cloaca. The groove, which is not 

 directly derived from pronephric funnels, gives rise to the abdom- 

 inal funnel ; the free process to the tube of the oviduct. At 

 first sight these facts seem quite irreconcilable with the account of 

 the development of the duct in the Elasmobranch ; but, if we reflect 

 that the kidney tubules and ducts are themselves outgrowths of the 

 coelomic epithelium, the difference does not appear so fundamental. 

 In the Elasmobranch the rudiments of both the pronephric tubules 

 and oviduct come off together and separate later ; in the Amniote 

 they appear separate from the first. Moreover, the distinction be- 

 tween the two modes of development is to some extent broken down 

 by what we know of the ontogeny of these organs in the Amphibia. 

 Here the Miillerian duct is formed to a greater extent from a groove- 

 like outgrowth, which grows backwards close to the pronephric 

 duct, and possibly to some extent is derived from the latter. The 

 oviducal funnel has been shown (Rabl [339], Hall [192a]) to be 

 either partly derived from (Salamandra) or developed in close 

 connection with the pronephric funnels (Amblystoma). 



It should not be overlooked that most of the speculations on 

 the homology of the oviduct have been biassed by our knowdedge 

 of its development in the Elasmobranch, which is more complete 

 and was earlier acquired than that of the origin of the oviduct in 

 other forms. The derivation of the Miillerian from the archinephric 

 (pronephric) duct may not be primitive at all, and it might well be 

 held that, whereas in all other Gnathostomes the oviduct develops 

 more or less directly from the coelomic epithelium, in the Elasmo- 

 branch alone has its rudiment become secondarily involved with the 

 rudiment of the pronephros. 



A knowledge of the development of these organs in the lowest 

 Teleostomes, and especially in the Dipnoi, would doubtless shed 

 great light on the subject. In conclusion it may be said that : 

 throughout the Craniata the mesonephric duct is the converted 

 archinephric (pronephric) duct ; and that the oviduct (Midlerian 



