CHAPTER XII 

 riTNESS OF TEMPERATURE CONSTANCY 



In his '* Lemons sur les phenomenes de la vie" Claude 

 Bernard concluded that '*all the vital mechanisms, varied 

 as they are, have only one object, that of preserving con- 

 stant the condition of life in the internal environment," 

 the blood — a very sagacious statement which has received 

 much support from recent investigations. The evolution 

 of the higher forms of life has been accompanied by a 

 gradually increasing independence of environment. This 

 has been achieved by the creation and maintenance within 

 the bodies of such animals of a suitable environment for 

 their constituent cells. The means by which animals 

 have reached this state of independence is through in- 

 crease in the cooperative functioning of their diverse 

 tissues. This evolution has passed through four signifi- 

 cant stages, which received their impetus from two evo- 

 lutionary events — migration from salt water to fresh 

 water and migration from water to land. 



A properly balanced nutrient level was early estab- 

 lished in the Metazoa about their body cells. By means 

 of this the higher Metazoa acquired a considerable degree 

 of independence in relation to fluctuations in their supply 

 of nutrients. The sea offers^ a considerable degree of 

 stability as an animal habitat. This is especially true 

 in respect to its food resources. A nutrient level or 

 reserve was not as essential for the maintenance of an 



