128 GENERAL ZOOLOGY 



Some of them are so small that no one has thought them im- 

 portant until recently. Yet several are so important that 

 death is sure to follow their removal. The thyroid and para- 

 thyroid are located in the neck region of man and of many 

 other vertebrates. A lack of iodine in the food causes the 

 thyroid to swell in a disease called goiter. Years ago many 

 operations for the removal of the thyroid in cases of goiter 

 proved fatal. This was because other small glands of ex- 

 treme importance were removed accidentally in taking out 

 the thyroid. These are the parathyroids. 



The hypophysis lies on the ventral side of the brain just 

 above the roof of the mouth. This minute gland regulates 

 growth. Giants are overgrown because of too active a 

 hypophysis. At the upper end of each kidney there is a 

 small gland called the suprarenal. Among other functions 

 this gland controls blood pressure and in critical situations 

 produces secretions that stimulate the body to unusual 

 action. Within the reproductive organs, or gonads, there are 

 important cells which have no part in forming germ cells. 

 These so-called interstitial cells regulate the development of 

 secondary sexual characters, such as the spurs of the rooster 

 or the beard of man. 



These few instances of functions give but an introduction 

 to the understanding of these ductless glands. Though 

 their functions are not fully understood, we do know that 

 growth and development and the functioning of many organs 

 are largely controlled by these glands. Even the character 

 and personality of an individual are greatly influenced by 

 them. 



