THE URO-GENITAL SYSTEM 385 



As a result of this, those parts of this latter system which have 

 been previously employed for reproductive purposes are re- 

 tained and even become more highly specialised, while the parts 

 that were wholly urinary disappear, with the exception of a 

 few vestiges. 



In this the two sexes are affected differently, as may be made 

 clear by a reference to Fig. 109, in which a and b show the 

 changes produced in the male, c and d those in the female. 

 In the male amphibian the sexual parts^are the testes, the vasa 

 efferentia and the mesonephrotic duct; in the male amniote 

 these parts are retained while the remainder of the mesone- 

 phrotic system has disappeared, being replaced by the meta- 

 nephrotic. The mesonephrotic duct, released from all urinary 

 function, becomes the definite ductus deferens, and the re- 

 maining portion of this system, including vasa efferentia, 

 sexual kidney ana collecting efferent tubules, becomes closely 

 associated with the testes under the name of the epididymis. In 

 the female amphibian the reproductive system has become prac- 

 tically independent of the urinary through the development of a 

 separate excurrent duct, the oviduct, and thus, with the rise of 

 the metanephrotic system, that of the mesonephros becomes 

 reduced to a few functionless vestiges ; yet the more conserva- 

 tive embryonic history records the fact that both oviduct and 

 ostium were originally portions of the mesonephrotic system, 

 and, although with a different history, both sexes are in reality 

 about equally indebted to it for their accessory organs. 



Although the reproductive organs, as given in the above 

 sketch, are the common heritage of all amniotes, the separate 

 groups of reptiles, birds, and mammals have been left to work 

 out the details in accordance with their own necessities. In 

 each there is a metanephrotic urinary system, with kidneys 

 and ureters distinct from the reproductive system except for 

 intimate topographical relationships at their outlets; in the 



(A) Male anamnian. (B) Male amniote. (C) Female anamnian. (D) Female 

 amniote. 



t, testis; o, ovary; ms, mesonephros; c, that part of the mesonephros which is 

 associated with the germ gland, (in male amniotes this becomes the epididymis); 

 t, Wolffian duct (ductus deferens); in, Miiller's duct (oviduct; mu, uterus); k, 

 metanephros; b, bladder (of the Amniota) ; n, ureter; r, rectum; v, vagina. 



