§ 3 OVO-FOLLICULAR SYSTEM 93 



The y-stage has the following characteristics:— 

 (i) beginning of the degeneration period; 

 (ii) formation of an orange-yellow pigment in the granu- 

 losa cells; 

 (iii) migration of the cells and necrosis. 



d. The d-stage. After this spontaneous migration the 

 remaining cells disappear. The nuclei become pycnotic and 

 form long threads; the cytoplasm disintegrates. In the end 

 only a light yellow mass of tissue remains to mark the former 

 presence of a corpus lutcum (Fig. 68). With this the span 

 of life, so full of variation, of the corpus luteum in the bit- 

 terling is terminated. 



As we have seen, the actual secretory glandular tissue in 

 the bitterling, like that of the corpus luteum in mammals, 

 originates in the granulosa layer. This is characteristic only 

 of the genuine corpus luteum; for in the case of the atretic 

 follicle or the atretic corpus luteum, the glandular tissue arises 

 in the theca interna. Whereas, in mammals, the corpus luteum 

 is formed after ovulation from the follicular wall, corpus 

 luteum formation in the bitterling already begins before 

 ovulation, and the ovum is sacrificed. We would, therefore, 

 give the name "pre- ovulation corpus luteum'' to the type 

 found in the bitterling, in contradistinction to the "post- 

 ovulation corpus luteum'' found in Sauropsidans and mam- 

 mals. 



It will be seen later that the pre-ovulation corpus luteum 

 constitutes an integral part of the ovaries of all anamnia, 

 reptiles and birds, and that, in these animals, it also plays 

 an important part in their sexual-endocrine system. 



§ 3. THE OVO-FOLLICULAR SYSTEM 



As a result of further research it was shown that not only 

 the bitterling but also other non-mammalian vertebrates 

 possess secretory corpora lutea (BrETSCHNEIDER (Selachii, 

 Teleostii, Amphibia, Reptilia) ; VAN Egmond (Selachii); 

 Jaski (Lebistes); Kristensen (Zoarces), and LEVER 

 (Serinus)). 



