152 ECONOMIC ZOOLOGY AND ENTOMOLOGY 



internal systems of organs undergo as radical changes as the 

 external parts. Muscles, salivary glands, parts of the alimen- 

 tary canal, etc., of the larva break down and are used as food by 

 new growth centers which develop into new muscles, new 

 salivary glands and other new internal parts. This internal 

 degeneration of larval parts and rebuilding of imaginal parts are 

 called histolysis and histogenesis, and form a fascinating subject 

 of study, which requires, however, a training in histologic 

 methods of technique beyond that of the elementary student. 

 In the next chapter, which is devoted to the classification of 

 insects, we shall point out the character of the metamorphosis 

 and some of the special features of development presented by 

 each of the different insect orders. 



