CYCLIC CHANGES IN THE OVARIES AND UTERUS OF THE SOW, ETC. 133 



lutea of pregnancy (known to be of the seventh and tenth days after parturition) 

 which were briefly mentioned in the previous paper (Corner, 1919) are quite similar 

 in microscopic appearance to those of the non-pregnant sow of the same relative 

 period of retrogression; it is very likely, therefore, that there is no difference in the 

 mode of degeneration of the two types of corpora lutea. 



What is given above is the first attempt, except for that of Leo Loeb (191 la), 

 dealing with the guinea-pig, to describe the histological details of retrogression of 

 the corpus luteum from specimens of known age, and in view of the somewhat 

 unorthodox result one is disinclined to enter upon a discussion of its general bearing, 

 except in a tentative way. It may fairly be said, however, that should the writer's 

 views of the structure of the corpus luteum, especially with regard to the fate of the 

 theca interna, be borne out by other work, they will afford a means of reconciling 

 one of the old disagreements of ovarian histology. It has often been pointed out 

 that in cellular arrangement the theca interna of atretic follicles rather closely 

 resembles the corpus luteum. Both tissues consist of large lipoid-laden cells sup- 

 ported by a reticular framework, with a rich capillary blood-supply. In the later 

 stages of retrogression the two tissues are indeed confusingly alike, and, in the 

 writings of Paladino (1879), Clark (1898), and many others, this fact has been one 

 of the mainstays of the theca-origin theory of the corpus luteum. This idea (in 

 connection with the view now held by nearly all investigators, that the so-called 

 "interstitial cells" found in some mammalian ovaries are derived from the theca 

 interna of atretic follicles) has been the basis of various attempts to correlate these 

 three elements of the ovary, such, for instance, as that of Ancel and Bouin (1909). 



Sobotta (1896), however, with his clear-cut demonstration, now generally 

 accepted, that the granulosa layer of the follicle takes a very important part in 

 corpus-luteum formation, could not agree to any statement of resemblance between 

 the two type's of follicle-derived tissue, and so expressed himself, when participating 

 in a general discussion of the fate of the corpus luteum at the 1908 meeting of 

 the Anatomische Gesellschaft. According to his description of events, in the 

 corpus luteum the granulosa persists and the theca interna is used up in the pro- 

 duction of connective tissue, while in atresia, of course, the granulosa breaks down 

 and the theca proliferates. 



Following, on the other hand, the present writer's account of formation of the 

 corpus luteum, and assuming that atresia folliculi, which has not yet been ade- 

 quately studied in the pig, is the same here as in other species, it will be seen that 

 the two processes differ in their course, but not greatly in their end-stages. The 

 granulosa cells, which degenerate in atresia, degenerate also in retrogression of the 

 corpus luteum, after their temporary metamorphosis into granulosa lutein cells; 

 while the theca interna cells, which by our account do not revert to fibroblasts 

 when they enter the developing corpus luteum, persist alike in the degenerating 

 corpus and in the atretic follicle. In this way the cells of the membrana granulosa, 

 derived presumably from the "germinal epithelium," are associated with the 

 ovum rather than with the soma, and those of each follicle run their course and 

 disappear when their own particular ovum leaves the body, either by degeneration 



