ORIGIN OF THE CORPUS LUTEUM 165 



mium tetroxide, but leave vacuoles of varying sizes, between 

 which a few stained granules may remain giving a character- 

 istic foamy appearance to the cytoplasm (fig. 19) ; and in 

 others practically all the fatty bodies and vacuoles have dis- 

 appeared, leaving a smooth homogeneous cytoplasm. In or- 

 dinary stained sections, then, the theca interna cells are of 

 about the same size as before rupture, their nuclei are perhaps 

 slightly more vesicular, and the cytoplasm is either homogeneous 

 or contains many densely packed vacuoles, usually uniform in size 

 within any one cell, resulting in the foamy appearance. 



Fig. 19 Theca interna cells of corpus luteum in stage of invasion, osmium 

 tetroxide fixation without further staining, showing varying degrees of fatty 

 inclusion. X 1000. 



It will be obvious that the previous clean-cut distinction be- 

 tween the two layers is now lost. Heretofore we have been 

 able to distinguish them by position, size, and content; there 

 has been a wall of connective-tissue fibrils between the layers; 

 the cells of the granulosa have been smaller than those of the 

 theca interna ; and the former have contained but small numbers. 



Fig. 18 a, Part of wall of developing corpus luteum in stage of invasion (ova 

 in tubes). Bouin fixation. Mallory's connective-tissue stain. X 110. b, En- 

 larged view of portion of same as indicated by rectangle. Mallory's connective- 

 tissue stain. X 1000. gr.l.c, granulosa lutein cells; th.l.c, theca lutein cells; 

 th.int., portion of original theca interna, near a fold in wall of corpus luteum; 

 b.v., blood-vessel. 



