544 MANUAL OF HISTOLOGY. 



there formed both ova and Graafian follicles, but the manner in which the 

 process is carried on is the same as before, " ova chains" appear anew. 



The origin of these remarkable structures is a question of great interest. 

 Pfluger was the first to point out that they were probably derived from 

 in-growth of the epithelium on the surface of the ovary, in the form of 

 tap-root like processes, and Waldeyer has since proved his supposition to 

 be correct. 



In suitable preparations (fig. 536) it is a matter of no difficulty to dis- 

 tinguish the growth downwards into the connective-tissue susteritacular 

 tissue beneath of the germinal epithelium at certain points (b). In 



Fig 536. 



the middle of such cellular masses certain large elements or primordial 

 ova are to be seen (c). Then by constriction at the surface of the organ 

 the follicle chain, or ova chain, represented in fig. 535, is produced. 



Thus, then, is the ovum formed. 



But what becomes of the ova ? Their destiny is twofold, one during 

 the period of immaturity of the animal, another all through the period of 

 generative activity. 



In the first period it would appear that both follicle epithelium and 

 ovum are frequently destroyed by fatty degeneration (Slavjansky). In 

 very young and healthy mammals, moreover, I myself have not unfre- 

 quently observed an extensive colloid metamorphosis of the whole con- 

 tents of the follicles. 



But the destiny of the ovum is quite different in the mature animal. 

 Here containing the material for the construction of a new individual, it 

 is destined to become free by bursting of the Graafian follicle. 



It was formerly believed that the stimulus of connection with the male 

 was requisite, as a rule, to bring about this rupture. Hence those who 

 held this view regarded the Graafian vesicles as persistent structures, of 

 which only a certain limited number ever really did burst during the 

 reproductive period of female existence. 



Recent investigation, however, has thrown quite a new light on this 

 subject. We now know that the expulsion of an ovum takes place with 

 every menstruation in the human female. It is, therefore, independent 

 of sexual intercourse, since this occurs in virgins as well as in married 

 women. Amongst the lower animals the period of heat, or rutting, is that 

 in which either one or more ova are liberated. 



