54 MORPHOLOGY OF THE VERTEBRATE BODY 



only tubules and blood vessels cut at various angles. The 

 function of the kidneys is to remove certain waste materials, or 

 excretions, brought to them by the blood from all parts of the body. 



The male reproductive organs of the frog consist of a pair of 

 testes which are suspended from the ventral face of either kidney 

 by mesenteries (Fig. 30). Within these testes, the male germ cells, 

 or spermatozoa (Fig. 212, p. 402), are produced. Small ducts, 

 the vasa efferentia, lead through the mesenteries of the testes to 

 connect with the kidney tubules. In this manner the sperma- 

 tozoa pass through the kidney tubules and ureters to the cloaca. 

 In some species of frogs there are pocket-like outgrowths of the 

 ureters, forming seminal vesicles in which spermatozoa are stored 

 in advance of the breeding season.^ At the time of sexual union, 

 the spermatozoa are passed from the anus and fertilize the eggs 

 just after the latter leave the female. Lying along the body wall, 

 lateral to the kidneys, and extending posteriorly beside the ureters 

 to the cloaca, are the rudimentary oviducts of the male, which are 

 structurally comparable with the functional oviducts of the female. 

 In the leopard frog they persist as conspicuous organs even in the 

 adult male, but in many other species they are recognizable in such 

 proportions only during an earlier stage of development. As 

 rudimentary structures, they may be compared with the mammary 

 glands of a male mammal, since they have a known use in only one 

 sex. 



The female reproductive organs (Fig. 30) consist of the ovaries, 

 which produce the female germ cells, the eggs or ova; and the 

 oviducts, by which these ova are conveyed to the cloaca. Each 

 ovary is a many-lobed mass, so much larger than a testis that it 

 seems upon superficial examination to be wholly different in its rela- 

 tionship to neighboring parts. When, however, one examines the 

 actual relationship, or better a younger stage in which the ovary 

 is small, it is seen that the ovaries, like the testes, are attached to 

 the ventral face of either kidney by mesenteries. There are, of 

 course, no ducts through the mesenteries to the kidneys comparable 

 with the vasa efferentia of the male, since the female system has its 

 oviducts; but in other respects the ovaries and testes are similarly 

 related to the other organs of the urino-genital system. The 



^ In the bullfrog, Rana caiesbiana, and the leopard frog, R. pipiens, the sem- 

 inal vesicles are inconspicuous. In the European form, R. fusca, they are 

 well developed. 



