DEVELOPMENT OF THE LEOPARD FROG 



401 



the ova that have been matured for a given season burst through 

 their coverings of cells (c/. Fig. 210) and through the outer wall 

 of the ovary, to become free in the ccslomic cavity. In the coelome 

 they are carried by the ciha of the peritoneum to the funnel-Uke 

 openings of the oviducts. The epithelium of the oviducts is also 

 cihated, and thus the eggs are conveyed to the ovisacs (cf. Fig. 30, 

 p. 52) at the posterior end of either oviduct, where they accumulate 

 before the act of laying. It is during their passage along the thicker- 

 walled and convoluted region, composing the greater portion of the 



0.4 



Fig. 210. — Section through a lobe of the ovary of the frog. 



b.v., blood vessel; c.o., cavity of ovary; f.c, nucleus of follicle cell; o.l, n.2, o.3, oA, a.id 

 0.5, stages in development of ova; p, pigment of animal hemisphere; t). p. .visceral peri- 

 toneum; W.O., wall of ovary. 



female duct, that they become coated with the gelatinous secretion 

 which is so conspicuous a feature of the eggs of frogs and other 

 Amphibia as they are usually found in the water. ^Vhen first 

 secreted by the oviducts, this jelly is merely a sticky fluid surround- 

 ing each individual ovum, but within a few hours after the eggs 

 enter the external water it becomes swollen and assumes the char- 

 acter of a thick gelatinous covering which persists until it dis- 

 integrates after the hatching stages of the tadpoles (cf. Fig. 11, 

 p. 23). When the jelly has thus swollen to its full dimensions (Fig. 

 211) it is seen to consist of two outer layers, of about equal thick- 

 ness, and a thin inner layer that is closely applied to the vitelline 

 membrane. The latter has by this time become completely sepa- 



