326 



CHORDATE ANATOMY 



of regulating the oxidation of carbohydrates in the tissues and the storage 

 of glycogen in the liver. How this is done is an unsolved problem. 



Pancreatic islands occur in all classes of vertebrates, usually in con- 

 nexion with the pancreas, though in some bony fishes the two glands are 

 independent. Both arise from the endoderm, but there is no evidence 

 that pancreatic gland cells are ever converted into cells of the islands. 



Male Sex Glands. It has long been known that removal of the gonads 

 in childhood prevents the appearance of secondary sex characters of the 

 male, such as beard, deeper voice, broadened shoulders etc. There is 



ANTERIOR /f PITUITARY 



BODY GROWTH 



i /•/ ^UTERU S >^ <^ \ CORPUS 

 FOLLICLE "^ ./;--gr^^«»*- - ^^^ =» ••wJ, LUTEUM 



Fig. 290. — A diagram of the interactions of pituitary, follicular and luteal hormones. 

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



plenty of evidence that hormones influence the secondary sex traits, the 

 first striking evidence appearing at puberty when the boy assumes some 

 of his adult male characteristics. Crew cites the case of a fowl which was 

 successively a mother and a father as a result of the destruction of the 

 ovary by disease and subsequent growth of a testis in place of the ovary. 



Female Sex Glands. In the ovary, as in the testis, interstitial and 

 germ cells may be distinguished. That the interstitial cells have an 

 endocrinal function is suggested by the fact that they increase during 

 pregnancy. The argument from analogy with the testis has less weight. 



Observed facts convince physiologists that at least two hormones, 

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



