CHAPTER X 

 THE RELATIONSHIPS OF INSECTS 



Classification may be defined as the orderly arrangement of different 

 objects into groups. Any articles can be classified in one way or another: 

 chairs for example, can be ])rought into groups acc(n"ding to the kinds of 

 wood of which they are made; or whether they are upholstered or not; 

 or according to their price, and any of these might be equally useful. 

 With living things, however, the problem becomes one of a "natural" 

 as opposed to an "artificial" classification. 



It is now the general belief that the first animals were extremely 

 simple in structure, and that in the course of generations (and centuries) 

 variation in their descendants led to the production of different forms, 

 and finally to all the multitudes of kinds now in existence. This devel- 

 opment has often been pictured as a tree, the trunk representing the 

 original animals, which, varying as individuals of the same kind always 

 do, began after a time to show several distinct lines along which the 

 variation took place. This would be represented in the tree by the lowest 

 branching of the trunk. Each main limb under the influence of the same 

 conditions would fork in its turn, perhaps into two, perhaps more, and 

 this process repeated again and again would finally produce the ter- 

 minal twigs — the present animals. Thus each twig would represent all 

 the individuals of the same kind; i.e., a single species; those nearest it 

 the other species most closely related to it; and those on another part 

 of the tree, though species and also related, would only be distantly so, 

 and of course, quite different. 



A natural classification of animals therefore, is an attempt to express 

 the actual relationships of the animals, placing nearest each other those 

 most closely related. To do this, the total of their differences and re- 

 semblances must be taken into account. Classification based on a single 

 character then, is almost always unreliable. The division of insects into 

 three main groups based on their metamorphosis, is an example of this, 

 for while it is entirely correct as a statement of facts, a classification 

 using this character would bring near together many insects which in 

 reality are only distantly related. 



The largest limb of the animal tree represents the original insects, 

 not because they were so numerous at first, but because they now form 

 such a large part of animal life. This limb is usually called a Class, 

 while the still more comprehensive groups considered in Chapter I are 

 called Phyla. These are the main divisions of the tree. In this case 

 the Hexapoda is the name given to the insect class. 



From all the evidence available, the original insects were at least 



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