CHAPTER II 

 BASIS FOR THE CLASSIFICATION OF ANIMALS 



If one is going to classify 600,000 different kinds of 

 animals, it will be necessary to have some general plan for 

 making large divisions which will include a considerable 

 number of species having common characteristics. To 



FIG. 12. A bit of cork showing cells as represented by Hook, the discoverer of 

 cells. (From Locy, Biology and Its Makers.) 



make a natural classification the seven following criteria 

 have been found of most value: 



1. Body Composed of One Cell or of Many. All living 

 things are made up of little living units, the cells (Fig. 12), 

 just as a brick house is made up of bricks. A cell, like a 

 brick, may thus exist as part of a structure or as an inde- 

 pendent unit. One great division of animals, Protozoa, is 

 made by grouping all those together whose bodies are com- 



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