532 INFLUENCE OF CLIMATE 



codile, boa, anaconda, the immense turtles of 

 the East and West Indies, as of the enormous 

 mollusca of the tropical seas, and the mighty 

 forests of India, Africa, and South America, is 

 fostered by the ceaseless influence of a power- 

 ful sun. 



If the whale and a few other mammalia attain 

 to a great size in high latitudes, it is because they 

 are supplied with an apparatus for obtaining 

 caloric from the atmosphere by respiration, 

 which maintains their mean temperature about 

 20 above that of the earth under the equator, as 

 will be noticed further hereafter. The caloric 

 thus acquired is preserved by means of a warm 

 fur coat, or a subcutaneous layer of fat, that in 

 the whale varies from eight to fifteen inches in 

 thickness. And if there be some species of 

 plants that remain evergreen throughout winter, 

 it is because they abound with oily and resinous 

 matter, which retains a sufficient amount of heat 

 to prevent the destruction of their foliage, but 

 not to maintain their growth. 



Now whatever the cause may be by which 

 organized bodies are enabled to renew their 

 composition, must determine the actions that 

 modify their structure and functions ; for the 

 elements of which they are formed are the same 

 in all parts of the world, with this prominent 

 exception, that within the tropics they are con- 

 tinually receiving from the sun a larger pro- 



