182 ELEMENTS OF COMPARATIVE ZOOLOGY. 



much eating increases rapidly in size. But since it is 

 enclosed in a hard outer wall, incapable of growth, it has 

 frequently to cast off this non-elastic "skin" and to grow 

 a new one, larger than the old. This molting is accom- 

 plished by a splitting of the old skin down the back, and 

 from this hole the animal draws itself, and now, its skin 

 being soft, it can readily increase in size. Gradually, how- 

 ever, the skin becomes thicker and harder, and the process 

 of molting must be repeated. With each of these molts 

 the animal grows more like the adult, the wings appearing 



FIG. 78. Young grasshopper with the wings just beginning to appear. 

 After Emerton. 



first as small pads upon the back, and with later molts 

 attaining the final size. It is an easy matter to follow 

 these changes by catching the young hoppers in the spring, 

 and keeping them in a breeding-cage, feeding them fre- 

 quently with fresh grass and leaves. The student must 

 keep this history in mind when studying the peculiarities 

 of the beetles. 



With few exceptions the Orthoptera are injurious to 

 human interests, since they are vegetable-feeders, and, as 

 they often occur in immense numbers, they can destroy all 

 crops throughout large districts. 



Possibly the most disagreeable members of the group are 

 the cockroaches, flattened forms,, many of them wingless, 



