164 THE URINOGENITAL ORGANS OF VERTEBRATES. 



The subsequent changes of these parts are different in the 

 two sexes. 



In the female the Miillerian ducts 1 persist and become the 

 oviducts. Their anterior ends remain open to the body cavity. 

 The changes in their lower ends in the various orders of Sau- 

 ropsida and Mammalia are too well known to require repetition 

 here. The Wolffian body and duct atrophy : there are left 

 however in many cases slight remnants of the anterior extre- 

 mity of the body forming the parovarium of the bird, and also 

 frequently remnants of the posterior portion of the gland as 

 well as of the duct.. The permanent kidney and its duct remain 

 unaltered. 



In the male the Miillerian duct becomes almost completely 

 obliterated. The Wolffian duct persists and forms the vas 

 deferens, and the anterior so-called sexual portion of the 

 Wolffian body also persists in an altered form. Its tubules 

 unite with the seminiferous tubules, and also form the epi- 

 didymis. Unimportant remnants of the posterior part of the 

 Wolffian body also persist, but are without function. In 

 both sexes the so-called permanent kidneys form the sole por- 

 tion of the primitive uriniferous system which persists in the 

 adult. 



In considering the relations between the modes of develop- 

 ment of the urinogenital organs of the bird and of the Se- 

 lachians, the first important point to notice is, that whereas in 

 the Selachians the segmental duct of the kidneys is first de- 

 veloped and subsequently becomes split into the Mullerian and 

 Wolffian ducts ; in the bird these two ducts develope inde- 

 pendently. This difference in development would be accurately 

 described by saying that in birds the segmental duct of the kid- 

 neys developes as in Selachians, but that the Mullerian duct 

 developes independently of it. 



Since in Selachians the Wolffian duct is equivalent to the 

 segmental duct of the kidneys with the Mullerian removed from 

 it, when in birds the Mullerian duct developes independently of 

 the segmental kidney duct, the latter becomes the same as the 

 Wolffian duct. 



1 The right oviduct atrophies in birds, and the left alone persists in the adult. 



