1905.] the Interstitial Cells of the Ovary in the Rabbit. 41 



and. the thinning of the chromatin strands, which become rather less in 

 number, as do also the nodules (fig. 4(c)). At the same time the granular 

 appearance extends gradually towards the centre, although it is not until 

 quite a late stage that it reaches the centre itself (fig. 4 (/) and (g)). The size 

 of the cell becomes gradually less, and the amount of protoplasm relatively 

 greater. 



The retraction, as it were, of the filaments and strands towards the 

 chromatin masses is very much more marked in the cells of smaller size, 

 where there is a tendency for the masses to pass towards the periphery, leaving 

 the centre clear (fig. 4 (d) and (e)). 



These changes continue until nearly all the chromatin is massed, the masses 

 becoming rounder as the process goes on. There are always traces of strand 

 formation left, in contrast to the protobroque nucleus, where it is markedly 

 absent. Thus the small cell derived by differentiation from the deutobroque 

 cell does not return to the characteristic protobroque type, but shows traces of 

 its intervening deutobroque condition in the shape of strands of chromatin, 

 and nodules on the strands. See fig. 4 (g). 



The cells, once reduced in size, become true ovarian cells, and may either 

 function as follicle cells or as interstitial cells (fig. 4 (h) and (&)). 



Thus we find the following processes taking place in connection with the 

 formation of the mature ovary. The cells of the germinal epithelium become 

 embedded in the underlying mesoblast, and, once there, may either undergo 

 differentiation, or apparently may remain in the protobroque condition. If 

 the former be its fate, it must undergo nuclear transformation, together with 

 growth in size, until it reaches the deutobroque stage. Arrived at this 

 condition it probably divides, although possibly this is not an essential, and 

 the two cells formed by this division are of the same type. There are now 

 two courses open for the cells thus produced ; they may undergo the nuclear 

 transformations of ovogenesis, and become primordial ova, or they may rest 

 for a time, and finally undergo regressive transformations, becoming either 

 follicle cells or interstitial cells. Every cell of the germinal epithelium is 

 probably a potential ovum, relatively very few remaining in the protobroque 

 state, although some may still be seen at the periphery in ovaries of the 

 eighteenth day. Incomparably the greater number pass to the deutobroque 

 state, preparatory doubtless to the formation of ova. All cannot become ova, 

 for the other forms of cell are necessary for the maintenance of the ovarian 

 functions ; possibly, therefore, only the most robust cells, and those which are 

 most conveniently situated for obtaining nourishment undergo the ovogenetic 

 changes. This would seem to be borne out by the fact that many more of 

 the central cells, which are nearer their food supply, undergo ovogenesis, than 



