30 NATURAL HISTORY OF INSECTS. 



resemble the adult or parent insect, with this exception, that 

 they are always destitute of wings (Fig. 65, c). After increas- 

 ing somewhat in size they cast their skins and appear in the 

 same form as before, except that a pair of small wing-pads is 

 usually to be seen there where the wings are to be in the per- 

 fect insect. At each succeeding moult, or casting of the skin, 

 the form still remains as before, except that the wing-pads are 

 growing larger (Fig. 65, g) till the insect moults for the last 

 time, when it appears with fully developed wings (as the 

 Chinch-bug, Fig. 85). All this time it has been able to move 

 about and to take food. 



When about its final moulting the larval insect firmly 

 fastens the hooks at the ends of its feet into some object; in a 

 short time the skin on its back splits open and the included 

 insect makes its escape. 



Insects which pass through their different stages in this 

 manner are said to have an incomplete transformation (meta- 

 morphosis). 



Some insects which are worm-like when they issue from the 

 egg are active to a certain degree while in the pupa state; 

 thus the pupa of the Lace-winged Fly, a short time before its 

 final change, issues from its cocoon and fastens itself by the 

 feet to some neighboring object; in a short time the skin on 

 its back is rent, and the perfect insect makes its escape. 



Some insects after issuing from the pupa are still enveloped 

 in a thin film-like skin; this stage is usually called the sub- 

 imago, and occurs among May-flies, and allied insects. They 

 usually fly to the nearest plant, or other object, and soon cast 

 off the film-like skin. 



A few insects, like the Blister-beetles (Fig. 86), appear to 

 pass through more than four stages. On the approach of 

 winter their larva casts its skin and appears in a different 

 form, commonly called the semi-pupa; it resembles the true 

 pupa in being unable to move about and to take food, but 

 differs from it in not having wing-cases, leg-cases, etc. In the 

 following spring it casts off its old skin, and appears once 



