96 FOLLICULAR DERIVATIVES IN VERTEBRATES III 



Stimulus meets only the basic tissues as elements from which 

 afterwards the gland is to be developed and organized. In this 

 process there is both disintegration and synthesis, the tissues 

 having to be turned into hormone-forming cells by means 

 of hyperplasia and hypertrophy. In fact, the corpora atretica 

 and corpora lutea are transitory, rhythmically-created and 

 only short-lived glands, whereas the other endocrine glands 

 are formed during embryogenesis, and destined to last the 

 whole of the animal's span of life. We must, therefore, attrib- 

 ute to the theca and granulosa a greater measure of auto- 

 nomy in the form of inherent potentiality, and to the 

 gonadotrophic stimuli a more active role than to the other 

 endocrinal tissues and their hormonal stimuli, respectively. 

 In the ovary these processes are on a higher plane, since here 

 new organs are to come into being, whereas, in other 

 endocrine glands, only the working rhythm is affected. In 

 the ovary, in addition to exciting and directing the secretory 

 function, the construction of the glands themselves is per- 

 formed. Herein lies an essential difference between the two. 



§ 4. THE POTENTIALITIES OF THE FOLLICLE 



The follicle of vertebrates possesses various potentialities, 

 which may be actualized through the cooperation of dif- 

 ferent factors, and may lead to the formation of various 

 follicular derivatives. The following factors are to be con- 

 sidered: (a) the moment at which the change takes place, 

 whether before or after ovulation; (b) the origin of the 

 tissue, whether it is the theca- or the granulosa tissue that) 

 is prominent; (c) the rupturing of the follicle; (d) the dual 

 anterior pituitary influence on (i) the epithelium, leading to 

 granulosa-luteinisation and (ii) the theca cells leading to 

 theca-luteinisation; (e) the presence of a critical period for 

 the tissues which are only able to respond at certain times. 

 Some part is further played by synergistic and antagonistic 

 correlations among the component parts of the ovary, and 

 between them and the pituitary, or between both of these 

 and the adnexa. Added to this, there may be overlapping of 



