CLASSIFICATION AND ADAPTATION 7 



in structure to maintain its life under the conditions 

 in which it Hves, the primary requirements being 

 food and oxygen. Every animal must be able to 

 procure food either of various kinds or some special 

 kind — either plants or other animals ; it may be 

 adapted to feed on plants or to catch insects or fish 

 or animals similar to itself ; its digestive organs must 

 be adapted to the kind of food it takes ; it must 

 have respiratory organs adapted to breathe in air or 

 water ; it must produce eggs able to survive in 

 particular conditions, and so on. 



One of the most interesting results of the study 

 of the facts of evolution is that each type of animal 

 tends to multiply to such an extent as to occupy 

 the whole earth and adapt itself to all possible 

 conditions. In the Secondary period reptiles so 

 adapted themselves : there were oceanic reptiles, 

 flying reptiles, herbivorous reptiles, carnivorous 

 reptiles. At the present day the Chelonia alone 

 include oceanic, fresh-water, and terrestrial forms. 

 Birds again have adapted themselves to oceanic 

 conditions, to forests, plains, deserts, fresh waters. 

 Mammals have repeated the process. The organs 

 of locomotion in such cases show profound modifica- 

 tions, adapting them to their special functions. One 

 thing to be explained is the origin of adaptations. 



It is, however, necessary to distinguish between 

 the adapted condition or structure of an organ 

 and the process by which it became adapted in 

 evolution ; two ideas which are often confused. 

 The eye would be equally adapted for seeing whether 

 it had been created in its actual condition or gradually 

 evolved. We have to distinguish here, as in other 

 matters, between being and becoming, and, further. 



