STRUCTURE OF THE VERTEBRATES 



261 



with the reproductive habits of the animal, which may be (1) 

 oviparous or egg laying; (2) ovo-viviparous, the retention of 

 large-yolked eggs until the embryo develops; or (3) viviparous. 

 In the last case the oviducts are specialized as uteri. The 

 urinogenital system then consists of two practically independent 

 systems: (1) the ovaries and oviducts; and (2) the kidney, 

 ureter, allantoic bladder, and urethra. 



The male amniote loses the Miillerian ducts during develop- 

 ment, a small posterior fragment remaining as the prostate 



Ovary 

 ^^Ostium 



Testis 



Vestigial 

 mesonephros 



Oviduct 



(Mesonephros) 



Vas deferens- 

 (Wolffian) 



Metanephros Metanephros 

 Ureter ^Ureter- 



■Bladder 



Female 



Bladder 

 Prostate 



Fig. 145. Structure of the Amniote Urinogenital System. Diagram (B), Fig. 

 144, shows the undifferentiated stage with both Miillerian and Wolffian 



ducts. 



gland which secretes a part of the seminal fluid. The meta- 

 nephros carries on the excretory function and the posterior por- 

 tion of the mesonephros disappears. The anterior portion of the 

 mesonephros, which functions in the fish and amphibia as a 

 sexual kidney, and the "Wolffian duct remain in the amniotes 

 as the efferent tubules and ducts of the testis. As in the anam- 

 niotes, the tubules burrow through the anterior part of the meso- 

 nephros into the testis, and these structures remain in the male 

 after the mesonephros degenerates. The mass of tubules in 



