184 ZOOLOGY 



Another way to regard the animals is from the stand- 

 point of the mode of life. Assuming that the first life 

 was aquatic, we can construct the following scheme, 

 again beginning at the bottom (see diagram, page 185). 

 Adaptation This diagram illustrates what Professor H. F. Osborn 

 calls "adaptive radiation," the tendency for life to 

 occupy all favorable situations, becoming modified to 

 suit the environment. It will be noted, however, that 

 there are limitations ; not all groups occupy all environ- 

 ments. 



