INTERSTITIAL CELLS OF MAMMALIAN OVARY 75 



in the cytoplasm toward the ovum in the cumulus, or toward the 

 antrum in other portions. With the degeneration of the ovum 

 in atresia, numerous lipoid granules appear in the follicle cells. 



In the fetal and postpartum ovary lipoid granules are abun- 

 dantly present in the medullary cords. They were recognized 

 first in my series in the 95-mm. fetus and from that time on ap- 

 pear to be constantly present in the indifferent cell masses which 

 do not immediately surround an ovum until such disappear from 

 the ovary before sexual maturity. In the period of develop- 

 ment of the peculiar medullary follicles (ca. 5 weeks) , it is interest- 

 ing to observe that in the irregular follicle, such as shown in figures 

 18, 24 and 25 in my previous paper, the epithelium immediately 

 surrounding the ovum is particularly clear from such free lipoid, 

 whereas the follicular epithelium of the remainder contains it in 

 abundance. This is easily demonstrable by means of osmic acid 

 fluids, and in preparations fixed and stained by the Weigert 

 hematoxylin method, the portion containing the greater amount 

 of lipoid stains much more intensely than the sheathing follicular 

 cells. In the 3 months ovary (fig. 3), containing the large irreg- 

 ular pluriovular follicles, the follicular epithelium bordering the 

 antrum and ova mainly lacks the free lipoid content. Many 

 of these Graafian follicles however possess irregular tubular ex- 

 tensions of the follicular epithelium, and the follicular cells com- 

 posing these contain free lipoid droplets. 



It is in the medulla in particular association with the free 

 lipoid containing medullary cords and irregularly developing med- 

 ullary follicles, that the groups of interstitial cells are found. 

 Figures 11 and 12 show medullary cords of a 3 to 4 day kit- 

 ten, illustrating the stromal investment, the 'loose' character of 

 the cells and the free lipoid content, some of which had doubt- 

 less been dissolved out before it was drawn, since it was from a 

 stained and covered series (No. 11). They likewise show the 

 modified, free hpoid-containing stroma cells, or in other words, 

 interstitial cells, and their close relation to the cells of the medul- 

 lary cord. 



During the period of growth of the medullary follicles, to the 

 interpretation of which considerable discussion was devoted in 



