CLASSIFICATION OF INSECTS. 115 



which we have already seen in the Glow-worm. Sometimes, as 

 in that instance, the deficiency of wings is confined to one of the 

 sexes usually the female ; whilst in other cases, both sexes are 

 destitute of these organs. Nevertheless there is a group, con- 

 sisting of three small orders, in which the want of wings is the 

 rule and not the exception ; and the insects brought together in 

 these, are associated together on account of their resemblance to 

 each other in general structure ; whilst, on the other hand, the 

 wingless insects first alluded to are left among the orders in 

 which they are placed, on account of their correspondence with 

 other insects of those orders in the structure of the mouth, the 

 nature of the metamorphosis, &c. 



637. We may divide the Class into two Sub-classes ; the 

 members of the first of which (A) always undergo some degree 

 of metamorphosis, and are usually possessed of wings in the 

 perfect state ; whilst those of the second (B) undergo no meta- 

 morphosis, and never become possessed of wings. From the first 

 sub-class may be separated one order, in which there are no 

 wings ; and there then remain eight principal orders, which are 

 classed according to the structure of the mouth and wings. 



SUB-CLASS A. 



Division a. Winged insects undergoing metamorphosis. 



Order I. COLEOPTEBA (Beetles). In these the mouth is 

 formed for mastication ; the anterior wings are converted into 

 hard elytra, or wing-cases ; the posterior wings are folded trans- 

 versely (or cross- wise) during repose; and the metamorphosis 

 is complete. 



Order II. ORTHOPTERA (Grasshopper, Locust, fyc.). In 

 these also the mouth is formed for mastication ; the anterior pair 

 of wings is composed of a substance more resembling parchment ; 

 the posterior pair, when in repose, is folded longitudinally (or 

 lengthwise) in the manner of a fan (Fig. 369) ; and the meta- 

 morphosis is incomplete. 



Order III. NETJROPTERA (Dragon-fly, May-jly)* In these, 

 too, the mouth is formed for mastication ; but the anterior pair 

 of wings, like the posterior, is membranous ; and the nerves of 



i 2 



