THE FINAL ADJUSTMENTS II5 



as we shall see, some of these effects can be brought 

 about by other non-specific substances. The hor- 

 mones are usually manufactured in special organs 

 set aside in the body for that purpose, which are 

 called the ductless glands, because they have no 

 opening to the exterior of the body but pour out 

 the substances they make directly into the blood- 

 stream. The ductless glands have all sorts of different 

 origins in development. For instance, the pineal 

 gland in man is formed from a structure which in 

 our remote ancestors was a third eye situated on top 

 of the head, and in its embryonic development traces 

 of this ancestry can still be found. One of the most 

 interesting of the glands is the pituitary, which is 

 built up partly from the ectoderm of the mouth 

 region and partly from the floor of the brain. It lies 

 well hidden in the skull, underneath the brain, and 

 seems to manufacture several different substances, 

 all of which are very active and important. One of 

 these substances has a great effect on growth. If it is 

 produced in too small quantities in a child, that 

 child becomes a dwarf, whereas if it is produced in 

 too large amounts, the child becomes a giant 

 (Fig. 29). Sometimes it is only in adult life that the 

 gland starts to produce too much of the growth- 

 controlling hormone, and then the main effects are 

 seen in the face, hands, and feet^ all of which become 

 very large and coarse, giving the condition known 

 as acromegaly. Other effects of abnormal amounts of 

 hormones are shown in Fig. 30. 



Hormones play an important part in animals 



