the Formation of the Corpus Luteum in the Sheep. 



139 



further hypertrophied, are now in places surrounded by a network of 

 fusiform cells. The point of rupture of the follicle is still open, and 

 communicates with the fluid-containing cavity. 



The epithelial cells of the corpus luteum of about fifty hours are 

 four or five times the size of those of the undischarged follicle, as seen 

 in section. Mitotic division is very rare among them, but evidence of 

 it may still occasionally be observed. Proliferation of the connective 

 tissue cells continues to take place, chiefly in the direction of the central 

 cavity, which has become smaller. Leucocytes are to be seen among 

 the epithelial cells, as well as free red corpuscles. The inner theca 

 layer, as such, has disappeared. The corpus luteum as a whole pre- 

 sents a radial appearance. 



The corpus luteum of sixty hours has undergone a further change. 

 The connective tissue cells are dividing in all directions, so that nearly 

 every epithelial cell is surrounded by an anastomosis of fusiform cells. 

 The central cavity also is completely enclosed by a layer of connective 

 tissue. The epithelial cells are still increasing in size by simple hyper- 

 trophy, but I have not observed any case of division. Large blood- 

 vessels, derived from those of the inner theca, may be seen in the 

 epithelium near the periphery. The corpus luteum is now larger than 

 the ripe follicle. 



The succeeding stages in the development of the corpus luteum 

 show the still further increase in the connective tissue proliferation, 

 and in the hypertrophy of the epithelial cells, and the consequent 

 growth in size of the whole structure. The dimensions of the develop- 

 ing corpus luteum are, however, no sure guide to its age, for I have 

 observed two in the same ovary and of the same age, but with an 

 appreciable difference in size. Blood vessels, at first enly to be 

 observed near the theca interna, spread towards the centre. The 

 cavity becomes obliterated by the inward growth of connective tissue, 

 and the point of rupture ceases to be visible. The connective tissue 

 becomes more and more finely distributed throughout the epithelium. 

 When the cells of the latter have attained a size of about six times the 

 dimensions of those of the unaltered membrana granulosa of the ripe 

 follicle, fatty degeneration sets in, and they become converted into 

 lutein cells. 



The above account of the development of the corpus luteum in the 

 sheep agrees substantially with that given hy Sobotta* for the mouse 

 and the rabbit, and by Stratzf for Tupaia and Tarsius. It differs from 

 Sobotta in the description of the part played by the theca externa, and 

 in recording the not infrequently observed multiplication of the epi- 



* Sobotta, "Ueber die Bildung des Corpus luteum bei c^er Maus," 'Arcliiyf. 

 Mikr. Anat.,' vol. 47, 1896 ; " Ueber die Bildung des Corpus luteum beim Kaninchen, 

 &c.," 'Anatomische Hefte,' vol. 8, 1897. 



t Stratz, ' Der geschle-jhtsreife Saugetiereierstock,' Haag, 1898. 



VOL. LXVIII. M 



