THE STRUCTURAL AND FUNCTIONAL SYSTEMS 55 



mesenteries of the ovaries are necessarily more extensive than those 

 of the testes, since they must support much larger organs and also 

 carry the many blood vessels that are necessary in pro\'iding the 

 blood supply for the growing ova. The oviducts are a pair of 

 much-coiled tubes communicating anteriorly with the coelome by 

 funnel-shaped openings, and posteriorly with the cloaca, as indi- 

 cated in the figure. The eggs leave the ovary by a rupture of its 

 surface and are thus, for a brief period, free within the coelomic 

 cavity. The action of microscopic structures known as cilia (Fig. 

 77 F, p. 141), aided perhaps by contractions of the body wall, con- 

 vey the ova to the anterior openings of the oviducts. As they pass 

 slowly along the oviducts, a fluid, which swells into the jelly sur- 

 rounding the eggs after they have reached the water, is secreted 

 about each individual ovum. It is believed that before the actual 

 laying can be accomplished all the eggs must have reached the 

 thin-walled sacs at the posterior ends of the oviducts, which 

 thus become greatly distended. During sexual union, the ova pass 

 from these ovisacs to the cloaca and out by the anal opening, where 

 they meet the spermatozoa that are being emitted from the anus of 

 the male. The union of one o\iim with one spermatozoon con- 

 stitutes fertilization. After the eggs have thus reached the water 

 in which they are laid and have been fertilized, the fluid secreted 

 by the oviducts becomes swollen to its final dimensions and forms 

 the jelly that surrounds the eggs and embryos in the early stages of 

 development. (Fig. 11, p. 23.) 



In Fig. 30 the female organs are represented on the left and 

 those of the male on the right, a condition which, of course, does 

 not occur normally in the animal, since the sexes of frogs are sep- 

 arate. Such a figure, however, shows by direct comparison the 

 resemblance between the male and female organization. The 

 ovaries are larger than the testes and of different structure, since 

 they produce ova and not spermatozoa. The ova reach the out- 

 side by special ducts and not through the kidney tubules and 

 ureters. Since the functional oviducts of the female are repre- 

 sented by non-functional, rudimentary oviducts in the male, it 

 appears that, aside from the differences between ovaries and testes, 

 the only structures in the male frog that are not present in the 

 female are the vasa efferentia, conveying the spermatozoa from 

 testes to kidneys, and the seminal vesicles which are present, in 

 some species, on the ureters of the male. 



