Chap. 34 



AMPHIBIANS 



709 



MOUTH OF ?- 

 OVIDUPT 



i^VIOUCT 



OVIDUCTS 



OPENING 



OF 

 VRETER 



.^LADDER 



CLOACA OP 



FEMALE 

 SIDE VIEW 



Fig. 34.23. Excretory and reproductive organs of the frog. Male and female. 

 Note the vestigial oviduct in the male. (Courtesy, MacDougall and Hegner: Biol- 

 ogy. New York, McGraw-Hill Book Co., 1943.) 



Each ovary is a lobed sac, with its interior divided by partitions into 

 chambers which are more or less filled with fluid (Fig. 34.23). It is covered 

 with epithelium continuous with the peritoneum of the mesentery (meso- 

 varium) that suspends the ovary from the body wall. Blood and lymph vessels 

 and nerves extend into it by way of the mesentery. The eggs originate from 

 certain cells in the lining of the ovary; certain others produce endocrine 

 secretions. As the eggs are enlarged with yolk, they project into the cavity of 

 the ovary. Cells in the lining of the ovary multiply and form a sac around each 

 growing egg (Fig. 34.24). Each follicular sac fits about the egg like a grape 

 skin around the pulp becoming a tighter fit as the egg reaches full size. Finally, 

 the egg is squeezed out of the sac, through the covering of the ovary and into 

 the body cavity. This process of ovulation occurs at about the same time for 

 the hundreds of eggs that mature in one season and leave the ovary within a 

 short interval. There are several factors which bring this about, among them 

 the secretion of endocrine glands chiefly of the anterior lobe of the pituitary 

 (Chap. 15). 



After ovulation, eggs fiU the body cavity but only briefly for they begin one 

 by one to pass into the funnels of the oviducts in a steady procession (Fig. 

 34.25). The funnels are small and are located on each side of the esophagus. 



