GENERAL CHARACTERISTICS. 365 



infancy, and much the longest, Insects are always wing- 

 less, pass most of their time in eating, and grow rapidly, 

 and the body, with some exceptions, is elongated, worm- 

 like, and consists of fourteen segments, one of these being 

 the head. For example, all caterpillars are butterflies 

 and moths in the larva state, or state of infancy. When 

 the larva has attained its full growth as a larva, it retires 

 to some concealed spot, and, in many cases, spins a silken 

 covering, called cocoon, casts its skin, and presents itself 

 as a much shortened, oblong, oval, F i g . 2 55 . 



or conical body, and apparently life- 

 less ; in this form it is called a. pupa 

 or chrysalis, and the period during 

 which the insect remains in this 

 state is called the pupa or chrysalis Cocoon 



period. At the end of this stage, which varies greatly 

 in duration, the insect again sheds its skin, and comes 

 forth fully grown, and, with few exceptions, provided with 

 wings, and in this state is called a perfect insect, or imago. 

 Thus, after insects enter upon the adult state, they no 

 longer increase in size, but, having provided for -a con- 

 tinuation of their kind, soon die. All insects which pass 

 through the changes pointed out above are said to under- 

 go a complete transformation. But there are some which, 

 although differing greatly in the young from the adult 

 state, do not pass through these changes ; but whose 

 larvae pass by more or less insensible gradations to the 

 pupa state, and from the latter to perfect insects, all the 

 while remaining active. All such are said to undergo 

 only a partial transformation. For example, the grass- 

 hopper is hatched from the egg as a wingless insect. As 

 it grows it casts its skin from time to time, becomes 

 proportionally longer, and in due time wings begin to 

 appear on the top of the back. It continues to eat 

 voraciously, grows rapidly, hops without aid of wings, 



