254 



How a Complex Aniinal Uses Food unit iv 



Fig. 244 T/.ie sex glavds of this silver-laced JVyandotte rooster (on the left) were 

 removed. As a result he changed into the hen-feathered bird shown on the right. 

 What is the difference in pliniiage? (u. s. bureau of animal industry) 



as acromegaly) is due to oversecretion 

 by the gland later in life. It is sometimes 

 treated by an operation on the gland. 

 With an undersecretion of the hormone 

 in a child, growth of the bones is stopped 

 at an early age; the result is a midget. In 

 cases of undersecretion M'hich are not too 

 severe, extracts of the pituitary gland 

 have been injected but so far without 

 much success. 



The pituitary — the "master gland." 

 The anterior portion of the pituitary 

 fjland secretes other hormones besides the 

 one which affects growth of the skeleton. 

 These hormones affect the reproductive 

 organs, the thyroid, the outer part of the 

 adrenals, and other ductless glands. That 

 is, the pituitary with its variety of hor- 

 mones has many important direct and in- 

 direct effects. Because of its influence on 

 so many parts of the body it has received 

 the name of the "master gland." 



The posterior portion of the pituitary 

 gland also produces several hormones. 

 They affect the body in various \\avs, 

 one of which is to stimulate the contrac- 

 tion of smooth muscles. You will remem- 

 ber that the walls of the digestive org^ans 

 contain smooth or involuntary muscle 

 cells. You have no direct control over 

 such muscles. But they "obey" this 

 pituitary hormone which comes to them 

 through the blood. The tiny muscles in 

 the walls of the arteries are also smooth 

 muscles; they too are made to contract 

 more violently by this hormone. 



Other ductless glands. It is not difficult 

 to obtain specimens of ductless inlands 

 from the butcher. Study them and an- 

 swer the questions in Exercise 5. In close 

 contact with the thyroid are the two 

 much smaller parathyroids. The secre- 

 tion of the parathyroids seems to have 

 something to do with the presence of 



