THE DEVELOPMENT OF THE CORPUS LUTEUM. 197 
The changes undergone by the discharged follicle have 
also been studied in various lower vertebrates. Bihler, 
who investigated the ovaries of Cyclostomes and certain 
Teleosteans, was unable to find any hypertrophy of the 
follicular wall, and Cunningham arrived at a similar con- 
clusion for the spent follicles of Teleosteans. The present 
writer has examined the discharged follicle of the common 
fowl without being able to detect any hypertrophy of the 
follicular epithelium. On the other hand, Mingazzini has 
discovered such hypertrophy in certain reptiles, structures 
resembling mammalian corpora lutea being found to occur ; 
while Giacomini, who has investigated the subject in birds, 
amphibians, and, more particularly, in elasmobranch fishes, 
also gives an account of the formation of corpora lutea by 
the hypertrophy of the follicular epithelium. The latter 
author describes and figures the corpus luteum of Mylio- 
batis as a glandular body in which the follicular epithelium 
is penetrated by an extensive ingrowth of connective tissue 
and blood-vessels. This account agrees substantially with 
what is found to take place in the mouse, the rabbit, and the 
sheep. A similar description is given by Wallace of the 
spent follicles in the fishes Zoarces and Spinax. Zoarces, 
however, presents a comparatively slight resemblance to the 
mammals in regard to this point, there being merely a slight 
hypertrophy of the follicular epithelial cells. In Spinax» 
on the other hand, there is a considerable hypertrophic 
enlargement of these cells, together with a thecal ingrowth 
at various points in a radial manner, and an ingrowth of 
blood-vessels. Lucein has also described corpora lutea in 
the reptiles Anguis and Seps, with which there is a simple 
hypertrophy of the cells of the follicular epithelium, un- 
accompanied by mitotic division. 
It thus appears that the follicular epithelial theory of the 
origin of the corpus luteum of mammals has been found to 
be true also for various members of the other vertebrate 
groups. 
The chief results obtained by the investigations of Sobotta, 
