THE FEMALE 43 



Finally, attached to the anterior end of the testis of the hibernating 

 frog may be seen finger-like fat bodies (corpora adiposa) which repre- 

 sent stored nutrition for the long period of hibernation, and for the 

 pre-breeding season when food is scarce. Under the microscope these 

 fat bodies appear as clusters of vacuolated cells, and are not to be 

 confused with the mesorchium. It is believed that they, as well as 

 the gonads, arise from the genital ridges of the early embryo. The fat 

 bodies tend to be reduced immediately after the breeding season, only 

 to be built up again as the time for hibernation approaches. 



The Female 



Secondary Sexual Characters 



The mature female frog is generally larger than the male of the 

 same age and species, the Rana pipiens female measuring from 60 to 

 1 10 mm. in length from snout to anus. The sexually mature female 

 has a body length of at least 70 mm. It can be identified by the ab- 

 sence, at any season, of the dark thumb pad; the inability to produce 

 lateral cheek pouches resulting from the croaking reaction; a flabby 

 and distended abdomen; and the presence of peritoneal cilia. These 

 cilia are developed in the female in response to the prior development 

 and secretion of ovarian hormones. 



Primary Sexual Characters 

 The Ovaries. 



The ovaries of the frog are paired, multi-lobed organs, attached 

 to the dorsal body wall by a double-layered extension of the peri- 

 toneum known as the mesovarium. This peritoneum continues around 

 the entire ovary as the theca externa. Each lobe of the ovary is hollow 

 and its cavity is continuous with the other 7 to 12 lobes. The ovaries 

 of the female are found in the same relative position as the testes 

 of the male but the peritoneum extends from the dorso-mesial wall 

 rather than from the kidneys, as in the male. 



The size of the ovary varies with the seasons more than does the 

 size of the testis. From late summer until the spring breeding season 

 the paired ovaries will fill the body cavity and will often distend the 

 body wall. They may contain from 2,000 {Rana pipiens) to as many 

 as 20,000 eggs {Rana catesbiana) , each measuring about 1.75 mm. 

 in diameter {Rana pipiens). The mature eggs are highly pigmented 



