450 



COMPARATIVE ANATOMY 



luteum persists throughout pregnancy and for some time subsequently. 

 If, on the other hand, the ovum is not fertilized, the corpus luteum degen- 

 erates in a few months and forms a transient structure, the corpus albicans. 

 Observed facts convince physiologists that at least two hormones, 

 the follicular and the luteal, are secreted by the ovary. The causal 

 relation between follicular secretion and menstruation is demonstrated 

 by the fact that menstruation follows the discharge of the follicular 

 secretion and ceases when the ovaries are removed. Furthermore, the 



ANTERIOR 



/ > 



PITUITARY 



I THYROID j 



/ 



/i\ 





o^ V^:>' 



FOLLICLE ^ //i--^:— »- ^«=ra=i^»Vw2 LUTEUM 



Fig. 375. — A diagram of the interactions of pituitary, follicular and luteal hormones. 

 (Redrawn after Dickinson's "Sex Anatomy," Williams & Wilkins Co.) 



follicular hormone, theelin, is used in cases of delayed menstruation and 

 puberty. Definite physical changes in a woman follow the menopause 

 when ovulation stops. Facial hairs tend to grow. Fat is deposited on 

 parts of the body. The breasts tend to atrophy. Nervous and mental 

 disturbances are likely to arise. 



A mature animal from which the ovaries are removed fails to manifest 

 the normal reproductive instincts, for example, estrus or "heat." An 

 immature animal which is ovariotomized fails to develop secondary 

 sexual traits, and remains throughout life infantile and sexually 

 neutral. Experiments indicate that estrus in animals depends upon 

 the follicular hormone. Follicular liquid injected into young female 

 rats brings them to sexual maturity in a few days. Injected into adult 



