412 



VERTEBRATE LIFE AND ORGANIZATION 



Fa.4; body 



Posterior ~i 

 vena cava. 



OvcLry 



Ovarian 

 mesentery 



Entrance oB 

 oviduct 



Cloaca. 



Oviduct 



Kidney 

 Adrenal 



^land 



y— Rena.1 vein 

 ^ Wolffian duct 



Ovisac 

 Urinary bladder 



Entrance of 



Wolffian duct 



Figure 21.14. Ventral view of the urogenital system of a female frog. The left 

 ovary has been removed. 



1 89. Reproductive System 



The reproductive system includes the gonads which produce the 

 gametes (eggs and sperm) and the reproductive ducts which transfer 

 the gametes to the exterior (Figs. 21.14 and 21.15). A pair of gonads, 

 testes in the male and ovaries in the female, are suspended by mesen- 

 teries from the kidneys, and a fingerlike fat body is attached to the 

 anterior end of each gonad. Since the fat bodies are largest in the fall 

 prior to hibernation, and smallest in the spring after mating, it would 

 seem that they serve as a reserve supply of food for the animal, and in 

 particular for the development of the gametes. 



In the breeding season, the ripe eggs are forced out of the ovary by 

 the contraction of smooth muscles in the wall of a saclike follicle which 

 surrounds each egg within the ovary. These muscle fibers are stimulated 



