200 WILLIAM WALLACE. 



fat-charged tissue of the follicular epithelium, according to 

 the extent to which the process of absorption has gone, 

 occurred in greater or less numbers in ovaries of all indi- 

 viduals examined, whether immature or mature. Ova of all 

 ages and sizes undergo absorption in this way. Embedded 

 in the tissue of the follicular epithelium in the larger 

 follicles, which, from their size, must originally have con- 

 tained a large yolked egg, are often seen masses of un- 

 digested yolk and remains of a broken zona radiata^ 

 Often there is a central mass of yolk separated by a space 

 from the encroaching tissue of the follicular epithelium, 

 which at this stage forms merely a thick lining to the egg 

 cavity. In this central mass of yolk, free cells, with nuclei 

 like those of the follicular epithelium, and probably derived 

 from this source, can be seen attacking the yolk. Many of 

 them consist of a vesicle containing a single fat globule. 

 The latter occupies nearly the whole cell, the cytoplasm 

 being reduced to a thin layer enclosing the globule. The 

 nucleus of these cells has been pushed to one side by the 

 development of the fat globule, and looks like a cap fitting- 

 over one end of the vesicle containing the drop. In other 

 free cells one may find several fat droplets in various degrees 

 of fusion to form a single globule. The mode of formation 

 of fat drops in these cells of the follicular epithelium is, 

 therefore, like what goes on in ordinary adipose tissue. In 

 the larger abortive follicles, in which the zona is tolerably 

 thick, the follicular epithelial cells have to soften and rupture 

 this membrane in order to gain entrance to the egg (fig. 22). 

 Cells of the follicular epithelium certainly do not pass through 

 pores in the zona, as has been sometimes asserted. That the 

 disintegration and solution of the egg membrane is due to 

 the action of the follicular cells is a conclusion that seems to 

 follow from certain observations on the degenerating eggs of 

 Zeus faber. In this species there are three egg mem- 

 branes, discounting the zonoid layer (tig. o-i). On comparing 

 ova of this species in various stages of degeneration it was 

 found that the outer layers of the egg membrane were first 



