HISTOLOGY 



153 



shaped nuclei with dark staining, coarse chromatin granules, surrounded by 

 very little, slightly basophilic cytoplasm, the fully developed lutein cells are 

 large and polyhedral with clear, slightly vacuolated eosinophilic cytoplasm 

 and large round vesicular nuclei. The change from one type of cells to the 

 other is gradual. The lutein cells are arranged in radial strands, surrounded 

 by a network of sinusoidal capillaries. By the time they become estab- 

 lished the central cavity has been obliterated. 



Corpora lutea. — As ovulation usually occurs spontaneously in rr.ice and 

 the presence of one set of corpora does not inhibit ovulation, the ovaries 

 may contain many sets of corpora lutea. According to Allen (2), ''The most 

 recent corpora lutea are easily distinguishable from the older ones by their 

 blue color, the latter staining more heavily with eosin." 



Deansley (26) conducted a detailed study of the fat accumulation in the 

 corpora lutea of the mouse during the estrous cycle. (The fat granules 

 were blackened by osmic acid preparation.) She found that in the corpus 

 luteum of ovulation the fat and lipoid contents of the lutein cells gradually 

 increase and that the granules become coarser as the next estrus approaches. 

 At the time of the next ovulation the granules are less distinct, and 2 days 

 after metestrus the cells contain hardly any fats or lipoids. Simultaneously 

 the cells become smaller and cell outlines are less distinct. The corpora 

 lutea of pseudo-pregnancy accumulate fat at a slower rate. Their cells are 

 slightly larger, and the nuclei are smaller. In the corpus luteum of preg- 

 nancy, fats and lipoids are absent until about the 8th day after copulation. 

 After that it contains finely distributed granules. The corpus enlarges 

 until about the 13th day (mean diameter 976 fj., nearly i mm.). After this, 

 little change takes place until about the i8th day when the corpus accumu- 

 lates fat and a gradual shrinking starts. At parturition the outline of the 

 corpus becomes indistinct and the fat and lipoid granules are coarser than 

 at any time before, but not as irregular as at the end of estrus or pseudo- 

 pregnancy. After parturition, although degeneration occurs, the body 

 persists for a considerable time. 



At the time of 10-12 days pregnancy, all the corpora lutea present in the 

 ovary (except those of pregnancy) rapidly degenerate, forming fibrous 

 masses containing large fat globules. 



During lactation the corpora of pregnancy show a gradual shrinkage. 

 During the first week the fats and lipoids show some increase, but this is 

 followed by a decrease and a loss of the regular distribution. At the end of 

 lactation diestrus (38 days after parturition) the corpora are fat free and 

 have a mean diameter of 480 ju. 



