GRAAFIAN FOLLICLES. 769 



The ovary appears very early in embryonic life, in the form of a cellular 

 outgrowth from the Wolffian body. Most of its cells are small, but as early 

 as the fourth or fifth day, in the chick, some of them are to be distinguished 

 by their large size, their rounded form and the presence of a large nucleus. 

 These cells are supposed to be primordial ova. In the process of develop- 

 ment of the ovary some of the peripheral cells penetrate in the form of tubes 

 (the so-called ovarian tubes) and at the same time, delicate -processes, formed 

 of connective tissue and blood-vessels, extend from the fibrous stroma under- 

 lying the epithelium and enclose collections of cells. It is probable that 

 there are two modes of formation of follicles ; one, by the penetration of epi- 

 thelial tubes from the surface, which become constricted and divided off into 

 closed cavities, and the other, by the extension of fibrous processes from be- 

 low, which enclose little collections of cells. By both of these processes, lit- 

 tle cavities are formed, which contain a number of cells. In each of these 

 cavities, there is a single, large, rounded cell, with a large nucleus, this cell 

 being a primordial ovum ; and in addition, in the same cavity, there are other 

 cells, which are the cells of the Graafian follicle. The exact nature of the 

 processes just described has been studied in the chick; but it is probable 

 that the same kind of development occurs in mammalia and in the human 

 subject. 



From birth until just before the age of puberty, the cortical substance of 

 the ovary contains several thousands of what are termed primordial follicles, 

 enclosing the primordial ova ; and it is probable that after the ovaries are 

 fully developed at birth, no additional ova or Graafian follicles make their 

 appearance. The prevailing idea is, indeed, that the great majority of these 

 never arrive at maturity, and that they undergo atrophy at various stages 

 of their development. In the adult, according to Waldeyer, the smallest 

 Graafian follicles measure -g-J-g- to -g-J-g- of an inch (30 to 40 /A), and the small- 

 est ova, a little more than ygVo" of an inch (26 /*). The primordial ova have 

 the form of rounded cells, each with a large, clear nucleus and a nucleolus. 

 Other structures are developed in and surrounding these cells, as the ova ar- 

 rive at their full development. 



The most important stage in the development of the ova and Graafian 

 follicles is observed at about the period of puberty. At this time a number 

 of follicles (twelve, twenty, thirty or even more) enlarge, so that all sizes are 

 observed, between the smallest primordial follicles, -gfa of an inch (30 /A), and 

 the largest, nearly an inch (12 mm.) in diameter. In follicles that have 

 attained any considerable size, there are the fully developed ova, one in each 

 follicle except in very rare instances, when there are two and these ova 

 have a diameter of about T |^ of an inch (200 /t). In the process which cul- 

 minates in the discharge of the ovum into the fimbriated extremity of the 

 Fallopian tube, the Graafian follicle gradually enlarges, becomes distended 

 with liquid and finally breaks through arid ruptures upon the surface of the 

 ovary. 



Fig. 276 shows the follicles and ova of various sizes. It is observed that 

 the larger follicles contain fully formed ova and have a proper, fibrous coat. 



