Metazoa Rana. 



327 



the cloaca by the rhythmic contractions of the muscular 

 fibres in the wall of the oviduct, while at the same time 

 glands in the upper region of the duct coat the ova with an 

 albuminous substance which swells readily in water. The 

 ova, as they are shed from the cloacal aperture, are fertilised 

 by sperms from the 

 male. 



Before describing 

 the subsequent de- 

 velopmental changes 

 which the fertilised 



FIG. 



182. FEMALE REPRODUCTIVE ORGANS OF THE 

 FROG. (Owen.) 



ovum undergoes it 



will be necessary to 

 glance at the origin 

 and development of 

 the sperms and ova 

 themselves, and also 

 at the changes which 

 take place in the 

 ovum before and in 

 the act of fertilisa- 

 tion. 



Both kinds of 

 reproductive glands 

 are at first precisely 

 similar ; they both 

 originate from meso- 

 blast (p. 249), and 

 both consist of what 

 is known as germi- 

 nal epithelium. In the male this epithelium arranges itself 

 in the form of a mass of convoluted tubules, which are 

 bound together by connective tissue. The cells lining these 

 tubules are spermatospores, or cells capable of forming 

 sperms. Each sperm originates as a bud (spermatoblasl) 

 from the spermatospore, the bud or daughter-cell having its 



a, oviduct ; o, ovaries ; 6, swollen end of the ovi- 

 duct with fertilised ova ; c, oviducal outlets into 

 the cloaca. 



