98 FOLLICULAR DERIVATIVES IN VERTEBRATES III 



a. Preliminary phase, termed the a-stage in our investiga- 

 tion of Rhodeus amarus (vide p. 82). We regard this as 

 the introductory phase, which, in the pre-ovulation corpus 

 luteum and atresia, consists of oolysis, and in the post- 

 ovulation corpus luteum and the calyx, of ovulation. It can 

 be shown in most cases that the ingression is a response to a 

 pituitary stimulus. 



^. The " organization- phase' ' ; this is formed by the hyper- 

 plasia and re-arrangement of the tissue into a gland. It 

 usually runs parallel with the a-phase. 



y. The functional phase, also called /3-phase, represents 

 the active phase of the gland, during which the hormone is 

 secreted. 



d. The regression phase, also called 7- and ^-phase, when 

 the gland is removed after the cessation of its function. This 

 brief process of creation, functioning and disintegration is 

 characteristic of the internally secreting glands of the ovary. 



a. Atresia. This is effected in the following manner:— 



a. a thecatrophic pituitary factor sets up hypertrophy in 

 the theca, producing luteinisation; 



y5. an epithelotrophic factor may either be absent or remain 

 without effect owing to the granulosa cell being blocked up; 



7. thecal substances (perhaps of an enzymatic nature) set 

 up, either directly or via the granulosa, oolysis and granulosa 

 degeneration. It frequently happens that the still intact gra- 

 nulosa prevents the luteinisation of the theca, whilst at the 

 same time the degenerating granulosa fails to check luteini- 

 sation, which would seem to point to a correlation between 

 these two tissues; 



d. the theca-lutein cells probably produce a sexual hor- 

 mone which acts upon the adnexa; 



£. the theca-lutein cells may persist as interstitial cells and 

 in this state also produce a sexual hormone, probably the 

 same (Fig. 71 A). 



b. The pre-ovulation corpus luteum is formed in the fol- 

 lowing way:— 



