532 TEXTBOOK OF ZOOLOGY 



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 lajdng. Recent 

 experiments have also shown that these fat bodies are essential for 

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

 ing their health. When they are removed, there is a deterioration 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 2^/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 than 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 

 1% to 2 inches. It usually takes about three to four years for this 

 young frog to attain maturity and begin egg laying. 



The embryology of the bullfrog does not differ materially from 

 that of the leopard frog, and the following account is based, except 

 where otherwise noted, upon the development of the latter. 



The egg when laid is a single cell. The upper portion of the 

 egg has considerable pigmentation, making it black. This part of 

 the egg is known as the animal hemisphere, and it is thought that 

 the pigmentation serves to absorb and retain heat necessary for 

 development. The lower portion is white and is known as the 

 vegetal hemisphere. The bullfrog egg is surrounded by a layer of 

 transparent jelly, but does not have an inner envelope of jelly, as 

 does the leopard frog egg. This jelly protects the egg and helps 

 it to retain heat. The nucleus of the egg, or germinal vesicle, lies 

 near the animal pole. The boundary of the egg is known as the 

 vitelline membrane. 



