132 CYCLIC CHANGES IN THE OVARIES AND UTERUS OF THE SOW, ETC. 



between lutein tissue and the surrounding capsule of connective tissue is now 

 obscured (fig. 6, pi. 1). In one or two of the animals there are great numbers of 

 polymorphonuclear leucocytes in the tissues and also mononuclear wander-cells of 

 the macrophage type, no doubt to serve the purpose of clearing away cellular 

 debris. 



The fate of the blood-capillaries is a matter of special interest in view of what 

 has already been said about the capillary endothelium as the source of reticular 

 connective-tissue fibrils. Deprived of much of their circulatory function by 

 abolition of the granulosa lutein cells, the capillaries for the most part collapse, with 

 nuclear degeneration in some cells, but remain in situ with the reticulum. There 

 is at first no increase in the total amount of connective tissue, though the decrease 

 in bulk of the corpus luteum crowds the fibrils into smaller space ; but as retrogres- 

 sion proceeds (fig. 5, pi. 1) the reticulum gradually becomes denser and thicker 

 until it gains an appearance like that of collaginous tissue, which is so characteristic 

 of the corpora albicantia (fig. 7, pi. 1). Whether in this change the endothelial cells 

 are gradually replaced by in wandering fibroblasts, or themselves retain the fibro- 

 blastic function, can not be said with certitude, but there seems to be no a priori 

 reason to doubt the latter possibility, in view of what we know of cellular dedif- 

 ferentiation in general. It may at least be definitely stated that the fibrous tissue 

 of the retrogressing corpus luteum is laid down in situ, for the Bielschowsky prepa- 

 rations make it clear that there is no direct growth of fibers from the surrounding 

 ovarian stroma into the corpus. 



It remains to discuss the fate of the cells of the third type, which the writer has 

 described as theca lutein cells. These seem, surprisingly enough, to survive the 

 blow which destroys the granulosa lutein cells; for among the debris and the col- 

 lapsed capillaries, and also in occasional clumps at the periphery, are found 

 numerous cells which, by reason of their usually angular or elongated shape, foamy 

 cytoplasm, and wealth of osmium-staining fatty material, can hardly be deemed 

 other than the theca lutein cells (figs. 15 and 16, pi. 2, th. I. c.). In one or two 

 animals the osmium preparations show numerous globules of blackened fatty 

 substance as large as 30 to 40 micra (represented, of course, in ordinary sections by 

 vacuoles) which seem to he in some of these same cells, suggesting that they, too, 

 are temporarily affected by the process of degeneration, to the extent of partial 

 fatty degeneration. When after a few days the nuclear fragments and the vacuolar 

 spaces left by the degenerated granulosa derivatives have disappeared (fig. 15, pi. 2), 

 the lipoid-laden cells are more clearly seen, enmeshed in the scar-tissue, where they 

 persist for weeks, acquiring even denser stores of yellow-pigmented fat (fig. 8, pi. 1) . 



By the time of a new ovulation the corpora lutea have diminished to 6 mm. 

 diameter, at the mid-intercestral period to 4 mm., and by the second ovulation 

 (i. e., when their own age is about 6 weeks) to 3 or 2 mm. Klipfer (1920) also finds 

 that they can be traced through a second interoestral period. After this they can 

 still be recognized in sections for at least another cycle of ovulation, but finally 

 become so obscure that they can no longer be certainly distinguished from atretic 

 follicles. It is interesting to note that the two specimens of retrogressing corpora 



