BANCROFT: OVOGENESIS IN DISTAPLIA OCCIDENTALS. 91 



is one resident within the follicle of the ovum, and this might lie 

 either in the outer follicular epithelium or the memhrana propria. I 

 think that at first both of these structures are the active agents; but 

 the irregular crowding together of the follicle cells in the corpus 

 luteum seems to show that, during the later stages of the process, at any 

 rate, the cells have no active function. Finally, then, by this method 

 of exclusion, we come to the membrana propria as par excellence the 

 active agent in forcing the ovum into the oviduct, and find that there 

 is considerable direct evidence for this view. In the first place, both 

 follicular epithelium and membrana propria are presumably under 

 tension in the largest eggs, being formed by the stretching of structures 

 that were formerly thicker and of less area. Secondly, the membrana 

 propria of the corpus luteum is perfectly homogeneous and quite thick; 

 and it is very improbable that a membrane which was formerly very 

 much thinner, and covered an area about fourteen times its present 

 extent could assume this condition unless it had been under tension, 

 upon the removal of which it could contract into its present shape. 

 Thirdly, it has the appearance of elastic substance, being thrown into 

 the folds characteristic of such material. These folds, however, may 

 in part be due to the irregular pull exerted on the membrane by some 

 of the follicle cells attached to it. When once the ovum is started on 

 its course up the oviduct, the continuation of its progress seems to be 

 effected by the contractions of the oviducal epithelium, but the main 

 force in the initiation of the process seems to be the elastic tension of 

 the membrana propria of the follicle. 



As soon as the ovum has entirely passed out of the ovary, the corpus 

 luteum begins to degenerate. The first change consists in the disso- 

 ciation of the deeply stained cytoplasm formerly associated with the 

 nuclei (Fig. 5). Strands of this material are still encountered, but 

 the characteristic arrangement is lost. At about the same time the 

 nuclei themselves appear paler, and the wandering mesoderm cells on 

 the surface of the structure are flattened against it, and together with 

 the membrana propria form an investing capsule (Fig. 5). Next 

 comes the constriction of the stalk of the corpus luteum, by means of 

 which it is separated from the stalk tissue. During this process the 

 lumen may or may not disappear, but after the distinct epithelial 

 connection with the stalk tissue is lost, the corpus luteum remains 

 connected therewith for some time by irregular strands of cytoplasm or 

 connective tissue. 



Within the isolated corpus luteum many vesicles are formed contain- 



