INTERSTITIAL CELLS OF MAMMALIAN OVARY 73 



is more granular, seemingly dgiser and becoming more dense 

 and homogeneous as the atresia progresses. The ovum early 

 shows an alteration, loses its spherical shape, becoming ellip- 

 soidal, as though affected by an increased intra-follicular pres- 

 sure. The follicular epithelum and theca, in early atresia show 

 in the cat no marked alteration. In later stages the follicular 

 cells become markedly spindle-shaped or stellate. Lipoid gran- 

 ules which (in the cat) are only scatteringly demonstrable in 

 the follicular epithelium become more numerous, typical kary- 

 olysis sets in, of the type early described by Flemming in this 

 kind of cell as chromatolysis, and the cells subsequently com- 

 pletely disappear. There is an undoubted 'invasion' of stromal 

 connective tissue and possibly of leucocytes as well. The liquor 

 becomes completely absorbed, and the antrum thus obliterated. 

 The egg cell disappears, the egg membrane (zona pellucida) per- 

 sisting for a long time (fig. 8). The last recognizable trace of 

 the follicle is the irregular ring of interstitial cells derived from 

 the theca interna. Ultimately this arrangement is broken up 

 under the stress of the growth changes within the ovary, and 

 there are but isolated groups of interstitial cells dispersed appar- 

 ently at random in the stroma. These finally, according to the 

 observations of Saimont and myself, revert to their original 

 stromal cell form. 



The relation of the interstitial cells to the atretic follicles is 

 strikingly shown in preparations in which osmic acid fixers, such 

 as Flemming's fluid, are used. The reproduction of typical sec- 

 tions is given in figures 4, 9 and 10, from which, -as in figures 5 

 to 8, of which they give the complementary 'lipoid picture,' the 

 relation of the interstitial cells to atresia is illustrated. Several 

 degrees of atresia are there shown. 



So consistently has this mode of thecal origin of the intersti- 

 tial cells of the adult ovary been supported by the observations 

 of nearly all who have devoted careful study to this phase of 

 the subject, that it may be accepted as clearly proven. 



I find therefore no support for the interpretation of Saimont 

 that (in his 3rd period) the interstitial cells are found as ''large 

 thecal cells in follicles that are undergoing development," but 



