724 GENERATION AND DEVELOPMENT. 



According to Bischoff, the number of the granules of 

 the yelk is greater the more mature the ovum, conse- 

 quently the yelk is more opaque in the mature, and more 

 transparent in the immature ova. The matter in which 

 the granules are contained is fluid in the immature ova of 

 all animals ; in some it remains so ; but in others, as the 

 human ovum, it subsequently becomes a consistent gela- 

 tinous substance. 



From the earliest infancy, and through the whole fruit- 

 ful period of life, there appears to be a constant formation, 

 development, and maturation of Graafian vesicles, with 

 their contained ova. Until the period of puberty, however, 

 the process is comparatively inactive ; for, previous to this 

 period, the ovaries are small and pale, the Graafian vesicles 

 in them are very minute, few in number, and probably 

 never attain full development, but soon shrivel and dis- 

 appear, instead of bursting, as matured follicles do; the 

 contained ova are also incapable of being impregnated. 

 But, coincident with the other changes which occur in the 

 body at the time of puberty, the ovaries enlarge, and 

 become very vascular, the formation of Graafian vesicles 

 is more abundant, the size and degree of development 

 attained by them are greater, and the ova are capable of 

 being fecundated. 



Discharge of the Ovum. 



In the process of development of individual vesicles, it 

 has been already observed, that as each increases in size, 

 it gradually approaches the surface of the ovary, and when 

 fully ripe or mature, forms a little projection on the exterior. 

 Coincident with the increase of size, caused by the augmen- 

 tation of its liquid contents, the external envelope of the 

 distended vesicle becomes very thin and eventually bursts. 

 By this means, the ovum and fluid contents of the Graafian 



