ITS MICROSCOPIC STRUCTURE. 53 



When the follicle enlarges at the time of heat, and before the escape of 

 the ovum, the cells floating in the fluid, and those forming the inner sur- 

 face of the theca, undergo a twofold transformation. Some merely he- 

 come elongated and present the various stages of transition into fibres, 

 while others become much enlarged in all directions, acquiring four or five 

 or even ten times their original diameter ; their nuclei at the same time 

 attaining double their former size, and presenting very distinct nucleoli. 



These enlarged cells are marked with granules of fatty matter of yellow 

 colour (fig. 4, B), some of these granules are contained within the cells, but 

 others are adherent, M. Zwicky thinks, to their outer surface while the 

 greater part lie free in the interstices of the cells. When the large cells 

 have attained their full size they either burst or become elongated, so as to 

 form fibres which are distinguished from the fibres resulting from the direct 



Fig. 4. 



transformation of the smaller cells, by their breadth, the large size of 

 their nuclei, and the presence of fat granules in them. Cells presenting 

 all these varieties of form may be found in the fully formed Graafian follicle 

 immediately previous to the escape of the ovum ; some floating in the 

 fluid contents, others forming plicse or villi on the inner surface of the 

 theca.* 



In a follicle from which the ovum has recently escaped, the theca is 

 thicker, and its inner strata are of a loose texture and red colour, and 

 consist chiefly of the large cells above described, mixed with some small 

 nucleated cells in part elongated into fibres, a few bodies resembling 

 the nuclei of the large cells, and numerous free, yellow, or orange coloured 

 fat granules. The external strata of the theca present no change from 

 their early condition. 



* It may be doubted whether these large cells are not altogether new formations. M. 

 Zwicky gives no very satisfactory evidence of their being even in part developed from the 

 small cells of the immature Graafian follicle. 



