FUNCTIONS OF ANIMAL ORGANISMS 



465 



In addition to producing the sex cells the gonads are also organs of 

 internal secretion, such secretions being produced by what are known as 

 interstitial cells lying in the framework of the gland and not belonging 

 to the germinal epithelium. The secretions of both the testis and the 

 ovary influence the development of the respective sex characteristics; 

 those of the testis affect sexual behavior in the male; and those of the 

 ovary control the rhythm of sexual activity and are active in bringing 



P/fu/ fary 

 bocty 



Parathyroicf 

 Thyroid 



Thymus 



•Adrenal 

 body 



Islets of Lang er- 

 hans in pancreas 



Fig. 299. — Diagram to indicate the location of the more prominent ductless glands in the 



human body. 



about the attachment of the fertilized ovum to the wall of the maternal 

 uterus. 



Other glands produce internal secretions which affect hasal metabolism. 

 This term is applied to the metabolic processes that continue all the time 

 in an animal, although it may be carrying on no digestive or voluntary 

 muscular activity; they are involved in the circulation, maintenance of 

 body temperature, and other vital processes. 



513. Excretion and Elimination. — In the process of excretion liquid 

 wastes are passed from all the cells of the body. The elimination of these 

 wastes takes place directly from the cells which form them only in the 

 lowest organisms; in higher organisms, as has been shown, organs and 

 systems are set aside for this purpose. 



