THE ANIMAL ORGANISM 



39 



of ovaries, which are attached by mesenteries to the body wall 

 at the level of the anterior end of the kidneys. Each ovary 

 has the appearance of a mass of black and white beads, which are 

 developing eggs. During the breeding season the ovaries 

 become so large as to exceed the rest of the viscera in volume. 

 The younger eggs or ova are small and white in color. As they 

 grow older, they become black at the animal pole and white at 

 the opposite, vegetative or vegetal pole, where most of the yolk is 

 concentrated. When mature, the eggs 

 are released by ruptures in the wall of 

 the ovaries and, propelled by the action 

 of cilia located on the surface of the 

 liver, pericardium, and peritoneum, 

 eventually find their way into the ovi- 

 ducts. Each oviduct is provided with 

 a wide mouth or ostium at its anterior 

 end, located near the base of the lung, 

 through which the eggs enter. As they 

 pass through the coils of the oviducts, 

 the eggs are covered with three layers 

 of an albuminous secretion of the walls 

 of the oviducts. At the lower end of 

 each oviduct, just before it opens into 

 the cloaca, an enlargement, the uterus, 

 serves as a storage place for mature eggs tive system of Rana pipiens, 

 before they are discharged through the ™t»' B ^SiJbJ^; 



cloaca (Fig. 17). F, fat body; K, kidney; 



The reproductive organs of the male ^^^Ur!^?.' ^^ 

 consist of two yellow, bean-shaped testes, 



attached by mesenteries to the body wall between the anterior 

 ends of the kidneys. Spermatozoa pass from each testis by way 

 of a small number of vasa efferentia into the corresponding kidney, 

 from which they leave by the ureter, a duct passing from the outer 

 border of the kidney to the cloaca. The ureter in the male thus 

 serves a double function in that it provides a passageway to the 

 cloaca for both the urine from the kidney and the spermatozoa 

 from the testis. In the male oviducts are present but reduced in 

 size. They are not functional (Fig. 18). 



The reproductive organs reach the height of their development 

 in the early spring when spawning occurs. The eggs are fertilized 



