ADAPTATIONS TO ENVIRONMENT 



WE saw in a previous chapter how the process of evolu- 

 tion led to a mastery of all the haunts of life. But it is 

 necessary to return to these haunts or homes of animals 

 in some detail, so as to understand the peculiar circumstances. of 

 each, and to see how in the course of ages of struggle all sorts of 

 self-preserving and race-continuing adaptations or fitnesses have 

 been wrought out and firmly established. Living creatures have 

 spread over all the earth and in the waters under the earth ; some 

 of them have conquered the underground world and others the 

 air. It is possible, however, as has been indicated, to distinguish 

 six great haunts of life, each tenanted by a distinctive fauna, 

 namely, the shore of the sea, the open sea, the depths of the sea, 

 the fresh-waters, the dry land, and the air. In the deep sea there 

 are no plants at all; in the air the only plants are floating bacteria, 

 though there is a sense in which a tree is very aerial, and the 

 orchid perched on its branches still more so; in the other four 

 haunts there is a flora as well as a fauna the two working into 

 one another's hands in interesting and often subtle interrelations 

 the subject of a separate study. 



I. THE SHORE OF THE SEA 



The Seaweed Area 



By the shore of the sea the zoologist means much more than 

 the narrow zone between tide-marks; he means the whole of the 

 relatively shallow, well-illumined, seaweed-growing shelf around 

 the continents and continental islands. Technically, this is called 



115 



