THE CLASSIFICATION OF ANIMALS 49 



really closely related may not, on the surface, closely resemble 

 each other. The outside of their bodies may become much 

 modified to adapt them to different environments. But their 

 internal structure and their development will usually reveal 

 their nearness or relation. On the other hand, animals not 

 closely related by descent may become and look superficially 

 like each other by becoming adapted to living in the same 

 environment, taking the same kind of food, etc. But again a 

 study of the development and internal anatomy will usually 

 establish marked differences, indicating their lack of real gen- 

 ealogic nearness. 



Modern zoological classification, is, therefore, based on a 

 great deal of serious study of animal structure and development 

 and represents, as we have already said, our present knowledge 

 of the actual blood relationships of animals. It means more 

 than that animals of the same group resemble each other in 

 certain structural characters. It means that the members 

 of a group are related to each other by descent, that is genealog- 

 ically. They are all the descendants of a common ancestor; 

 they are all sprung from a common stock. And this added 

 meaning of classification explains the older meaning; it ex- 

 plains why the animals are alike. The members of a group 

 resemble each other in structure because they are actually 

 blood relations. 



The history of animal classification with all the changes in 

 it, and the succeeding points of view and new significance 

 represented by these changes, is an interesting chapter in the 

 history of science. It began, in any real way, with Linnseus, 

 the great Swedish naturalist who worked in the middle of the 

 eighteenth century. In the years just before and after 1750 

 he published successive editions of his "Systema Naturae," 

 which was the first attempt to describe and name and classify 

 all the known kinds of animals and plants. In the loth edition 

 (1758) of this "Systema" he catalogued about 4000 kinds of 

 animals. (Now we know 500,000 kinds!) 



In this great catalogue he adopted a system of short scien- 

 tific names, one for each kind of organism. And he classified 

 all these named animals into groups of successive degrees of 



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