82 FOLLICULAR DERIVATIVES IN VERTEBRATES III 



The scanty information available concerning the histology of the ovary 

 of the fish occasionally contains references to the corpora lutea found by 

 us. Such formations, however, were believed to arise from degeneration of 

 the ovum. BUHLER (1902), (Petromyzon and Cotegonus) , and, more 

 recently, LYNGNES (1937), (Myxine) described the fate of follicles 

 remaining behind after ovulation. Both these writers were struck by the 

 fact that it is possible also for non-ovulated follicles to "degenerate", even 

 before the ovum matures. Both take this process to be what is known as 

 "ovular atresion", and find it to be merely the interruption of some 

 process of growth. LYNGNES describes in detail certain forms of "ovular 

 atresia" and is of the opinion that they are caused through damage to 

 ova as a result of the growth of other ova. 



These authors did not expect to find a close relationship 

 between the gonads and secondary sexual organs in anam- 

 nia, and so did not assume the occurrence of corpora lutea 

 with secretory activity. It was only through the expe- 

 rimental induction of growth in the ovipositor that the hypo- 

 thesis arose that there might possibly exist a connexion 

 between the ovary and the growth of the ovipositor. 



In the bitterling the corpora lutea develop chiefly from 

 the ovicular follicles of the third period of growth (500 — 

 1000 «). The process of disintegration of the ovum and of 

 its conversion into the corpus luteum may be divided into 

 four successive stages:— 



a. a-stage. The ovum is attacked by follicular cells, made 

 resorbable, and finally resorbed and phagocytosed. 



b. jS-stage. In the follicular cells a new substance is form- 

 ed, the lengthening hormone, oviductin, which is absorbed 

 by the blood. 



c. y-stage. Hormone production ceases when disintegration 

 is completed, the yellow lutein pigment remaining behind, 

 as cellular residue in the follicular tissues. 



d. d-stage. The resulting corpus luteum partly atrophies 

 into an irregular heap of cells, the majority of which are dif- 

 ferentiated into histiocytes (BretsCHNEIDER, DuyveNE DE 



Wit, 1 941). 



We will now examine the four stages separately in more 

 detail. 



a. The a-stage. Two factors indicate the transition from 



