96 ESSENTIALS OF ZOOLOGY 



The two oviducts are greatly convoliited 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 

 ostia, 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 ovarj^ and its peritoneal covering and are 

 free in the body cavity. They make their way to the 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 enormously when it contacts water. 



Fertilization in the bullfrog is external, and the spermatozoa of 

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



Attached to the anterior end of the testes of the male frog and 

 to the ovaries of the female are fingerlike projections known as 

 fat bodies. These serve to store a reserve fat supply which the bull- 

 frog may draw on during hibernation or at other times. They are 

 largest before hibernation and smallest after egg laying. Eecent 

 experiments have also shown that these fat bodies are essential for 

 allowing the normal development of the sex organs and for main- 

 taining their health. When they are removed, there is a deteriora- 

 tion of eggs and sperm . 



Embryology 



The bullfrog lays its eggs in a large floating mass, forming a sur- 

 face film on the water, usually among brush or plants near the 

 pool's edge. This mass may be from 1 to 2i/2 feet in diameter and 

 may contain ten to twenty thousand eggs. In Texas, bullfrogs may 

 lay their eggs as early as February, though it is more common for 

 them to be laid later in the season. 



The eggs of the bullfrog are smaller tha?i those of the leopard 

 frog. They hatch in about four or five days, depending on the tem- 

 perature. After hatching, the tadpole normally spends about two 

 years in the water before transforming as a young bullfrog. The 

 tadpole may grow to be four to six inches long, but the average 

 body length of the young bullfrog as it metamorphoses is about 



