Classification of Chorda tes 

 Protochordata 



^QAi 



11 



Animals in the wild are not classified. Forest, jungle, ocean — each 

 has its characteristic motley population. Animals with and without 

 backbones seem indiscriminately mixed. But it is a well-ordered pro- 

 miscuity. Each animal is in a biologic (ecologic) environment that fits 

 it. In the matter of food, for example, the animal is placed so that it 

 may get the other animals or plants which it needs, and — the inevit- 

 able converse of that — so that a certain proportion of those of its kind 

 may be eaten by others. The species of animal which cannot maintain 

 a balance between eating and being eaten disappears from the local 

 scene. 



Classification of organisms is a practical necessity for purposes of 

 describing and comparing them. Modern classification arranges ani- 

 mals according to those similarities and differences which may be 

 taken to indicate degree of genetic relationship. Such a classification 

 is, therefore, a summary of the findings of Comparative Morphology 

 (including Paleontology) working by the "method" described and 

 illustrated in the preceding chapter. 



Although the main lines of the classification of vertebrates are 

 fairly well established, there is still much difference of opinion as to 

 the best way of arranging and naming the groups. No two authors offer 

 classifications which are identical in plan and naming. While the 

 vertebrates are more fully known than any other large group, there 

 are still some whose systematic position is dubious. As a matter of 

 convenience, it seems necessary that every animal should be included 

 in a classification. Therefore animals of doubtful affinities are placed 

 according to the best judgment of the classifier — with the result, in one 

 case, that the "flying lemur" of the East Indies (Fig. 546) may be 

 found in any of three Orders of mammals. It might be better to set up 

 an unclassified class to include all the doubtful cases. 



389 



