SUMMARY 83 



Classification. — Just as we collected the different grass- 

 hoppers into the family Acrididae, and the grasshopper, 

 cricket, cockroach, and locust into the order Orthoptera, 

 so now we group all the animals we have studied into the 

 class insecta. As a representative of the family the grass- 

 hopper has certain characteristics; as a representative of 

 the order, certain other characteristics ; and as a member of 

 a class, the grasshopper and the others just studied have the 

 structures in common which have been outlined under the 

 head of similarities. 



But in the last comparison since the definition of the class 

 was found by similarities and the definition of the order 

 by the differences, we should find the differences now about 

 the same as the likenesses when we made our first compar- 

 ison. Find if this is true. 



How could we get similarities for the orders Coleoptera, 

 Hymenoptera and Lepidoptera that would be the same as 

 the differences we have found? 



The Social Life of Insects. — It has been noticed how 

 perfectly each animal is fitted for the sphere of life in which 

 it moves. Whatever it does it seems to be especially fitted 

 for doing. Thus the entire structure is specialized, some of 

 the organs in one direction and some in another ; but what- 

 ever may be the shape or texture of the organ, it helps the 

 animal to live in the surroundings in which it is placed. 



The difficulties of these surroundings are many and cause 

 every year the death of millions of insects, so that if some 

 provision were not made in the structure of the animal to 

 enable it to battle against these adverse circumstances the 

 entire class would become extinct. It is really then a battle 

 against death which the insects wage and their specialized 



