578 HERBERT M. EVANS 



for a little Mile still distinguishable from the granulosa elements, but 

 as the latter enlarge in a characteristic way to become converted into 

 lutein cells they also appear to partake of similar changes so that it is 

 finally difficult to distinguish the two cell types. From both internal and 

 external theca, fibroblasts grow into and amongst the inner thecal and 

 granulosa cells and sprouting capillaries also keep pace with the enlarg- 

 ing cells, which come finally to fill up the old follicular central space, so 

 that a solid, spherical epithelioid structure is created the corpus luteum. 



Undoubtedly the main mass of the yellow body is constituted by a 

 transformation of the granulosa cells, as was first made out convincingly 

 for the mouse by the classic researches of Sobotta and has been recently 

 apparently confirmed for man by R. Meyer, Wolz, Wallart, Timofeiev, 

 Strakosch, Reusch, Novak, and others. Yet, as we have indicated, the 

 enlarged internal theca cells would appear to form some of the lutein 

 elements (at least at the periphery of the corpus) as Van der Stricht was 

 able to show in the bat and clog and as has again been supported by the 

 studies of Corner on the histogenesis of the corpus in the sow. 5 



The peculiar structure which is thus formed as a successor to the 

 ruptured follicle has specific duties to perform, as has become clearly 

 established through the researches of Ludwig Frankel. 6 It accomplishes 

 this by pouring into the blood stream an internal secretion, the intimate re- 

 lations between lutein elements and the capillaries being typically adapted 

 to that end. The corpus luteum has a definite functional life cycle, though 

 it may persist for a long while in the ovary, and it constitutes one of the 

 most important even if transitory endocrin glands. Hormons from the 

 corpus luteum provoke distinctive changes in the remainder of the repro- 

 ductive and accessory reproductive organs of the body, changes which are 

 intimately connected with the proper provision for the fertilized ovum 

 and the new offspring resulting therefrom. 



Conditions in the Mammalia in General. Ovulation in Many 

 Mammals Rhythmic. In many mammals the events which we have just 

 described occur spontaneously at regularly repeated, fairly short intervals 

 so that we may speak of the ovulation cycle of the species in question. In 

 other cases, as Heape has shown, ovulation happens but once or twice per 

 year, at times presumably when Nature affords the best provision for the 



5 These are the "theca-lutein cells" of Seitz and others, so-called to distinguish them 

 from the chief or granulosa lutein cells. 



6 It is true that Friinkel's formulation of the dependence of menstruation on the 

 corpus luteum in the sense that the former was produced by the latter was erroneous: 

 but the premenstrual endometrium is so produced. He has been sufficiently castigated 

 by many subsequent workers and acknowledged the error of his ways if by no other 

 evidence than by his recent reformulation in the Liepmann Handbuch. This should 

 not cause us to overlook Friinkel's establishment of the connection between the corpus 

 luteum and the uterus both in the cycle and in implantation. The necessary pres- 

 ence of the ovary for menstruation had been demonstrated by the classic transplanta- 

 tion experiments of Halban. 



