reality atretic follicles that is to say, follicles which had undergone 

 degenerative changes without ever heing discharged. Thus, the 

 words used in a description given by Clark seem to indicate, that 

 this author was dealing with the degenerative epithelial cells of an 

 atretic follicle. It seems not impossible also that the young human 

 " corpus luteuin " described by Doering was a degenerate follicle ; 

 while Kolliker's opinion that the corpus luteum is an entirely 

 connective tissue structure appears to have been founded on the 

 assumption that the changes exhibited by discharged follicles and 



FIG. 41. Corpus luteum of mouse fully formed. (From Sobotta.) The luteal 

 tissue is vascularised and the central cavity filled in with connective tissue. 



retrogressive undischarged follicles are identical in character. It is 

 to be noted further that in the investigations of all those writers 

 who have upheld the connective tissue hypothesis, the ages of the 

 developing corpora lutea were unknown, the material having been 

 collected in no case by Sobotta's method of killing the animals at 

 successive intervals after coition. 



In 1901, after the publication of the papers referred to above, 

 the present writer issued a preliminary account l of an experimental 

 inquiry upon the formation of the corpus luteum in the sheep. In 

 this inquiry the animals were killed at successive intervals after 



1 Marshall, "Preliminary Communication on the (Estrous Cycle and the 

 Formation of the Corpus Luteum in the Sheep," /'/. /'<>//. >V., vol. Ixviii., 

 1901. The full paper was afterwards published in the Phil. Tr-i,,*., B., 

 vol. cxcvi., 1903. 



