CLASS AMPHIBIA 531 



Reproductive Organs 



The ovoid testes (Fig. 278) of the male bullfrog are attached to each 

 kidney by a fold of peritoneum. In this fold of peritoneum, running 

 between the testes and kidneys, are several small ducts, the vasa 

 efferentia. These ducts connect with the mesonephric duct through 

 the collecting tubules of the kidney. Spermatic fluid containing the 

 spermatozoa passes from the testes through the vasa efferentia into 

 the kidney, then into the mesonephric duct, which opens into the 

 cloaca, and thence to the outside through the anus. In some species, 

 this duct is slightly expanded prior to its opening into the cloaca to 

 form the seminal vesicle, a reservoir for spermatozoa. This is poorly 

 developed in the bullfrog. 



The two ovaries of the female bullfrog, when filled with eggs, 

 occupy a large part of the body cavity and consist of folded sacs 

 covered with peritoneum. They originate in about the same posi- 

 tion as do the testes and lie in a fold of the peritoneum ventral to 

 the kidneys. The eggs lie in the outer surface of the ovary and 

 during their growth are surrounded by a network of blood vessels 

 and follicle cells. 



The two oviducts are greatly convoluted white tubes, one on each 

 side of the body cavity, running from near the base of the lungs to 

 the dorsal wall of the cloaca. Their anterior ends are funnel-shaped 

 and open into the body cavity. Their posterior ends are dilated to 

 form thin-walled ovisacs or uteri which open into the cloaca near the 

 entrance of the mesonephric duct. They are not connected at any 

 point with the ovaries. 



When the eggs are mature at the breeding season, they break 

 through the walls of the ovary and its peritoneal covering and are 

 free in the body cavity. They make their way to the funnel-shaped 

 opening, or ostium, of the oviduct and, probably by ciliary action or 

 movements of the female, are squeezed into it. The oviducts contain 

 a large number of glands which secrete a clear, jellylike material. 

 As the eggs are forced down the oviduct by ciliary action, they 

 become coated with the gelatinous material, which swells enor- 

 mously when it contacts water. 



Fertilization in the bullfrog is external, and the spermatozoa of 

 Die male enter the eggs after they have been laid in the water. 



