ORIGIN OF THE CORPUS LUTEUM 143 



are notable for the presence in their cytoplasm of a number of 

 vacuoles, giving them a striking honeycombed appearance (fig. 

 4, b). These vacuoles are due, at least in part, to the presence 

 in the fresh tissue of granules of fat-like substance, packed closely 

 into the theca cells, whose chemical nature has not been deter- 

 mined (fig. 5, 6). In some species they are quite yellow, since 

 they hold in solution some of the lipochromes common in the 

 ovaries of certain animals, but in the pig they are practically 

 colorless. It is of course the appearance of these large fatty 

 cells of the theca which has helped establish the belief that they 

 are the precursors of the ' lutein cells' of the corpus luteum. The 

 granules are soluble in alcohol; in osmium tetroxide they take a 

 color varying from gray to deep black; they take a decided red- 

 dish color with Herxheimer's alkaline Scharlach Rot, but appear 

 not to stain at all with Nile-blue sulphate; they are not aniso- 

 tropic. From these reactions we may assume that the substance 

 is of lipoid nature, but is perhaps not a neutral fat. The gran- 

 ules are variable in diameter, from 0.5/x to 1.5ju, a few even 

 reaching 2.5/*. Many of the theca cells contain, instead of 

 lipoid granules, vacuoles which are not stained even in osmium 

 preparations, and which therefore must contain either a modi- 

 fied form of the lipoid or some other substance which is not ren- 

 dered insoluble by combining with Os0 4 (fig. 5, b). The smaller 

 cells of the theca interna mentioned above usually have finer 

 granules, but there are all transitions between the large and small 

 types. The cells of the granulosa contain a few very small 

 granules, uniformly black after osmium fixation; these are usually 

 more numerous in the basal layer of the follicular epithelium. 



Between the granulosa and the cellular layer of the theca in- 

 terna just described is a narrow zone (0.03 to 0.04 mm.), which 

 contains chiefly spindle cells without fatty inclusions or vacuoles 

 (figs. 4, a, and 5, a). These cells appear to be of two types: 

 first, the endothelium of the blood-vessels which lie in this zone 

 and, second, the fibroblasts of the perivascular tissue, which are 

 part of a light network of connective-tissue reticulum support- 

 ing the theca and forming a base for the granulosa, for I agree 

 with J. G. Clark that the membrana propria is nothing more 



THE AMERICAN JOURNAL OF ANATOMY, VOL. 26, NO. 1 



