76 HISTORY OF INSECTS. 



but from these, insects may at once be distinguished by 

 their being furnished with six legs and four wings ; they 

 also differ in wanting that singular property possessed by 

 crabs and lobsters, of rejjroducing a limb that has been ac- 

 cidentally lost. The great value of these characters is 

 proved by the imjjortance attached to the exceptions which 

 have been detected ; flies have two of their wings small 

 and imperfect ; butterflies have the first pair of legs unfit- 

 ted for walking; and a Dr. Heineken thought he found 

 something like a re-production of the antennae of cock- 

 roaches. The beings, therefore, of which the ' Grammar of 

 Entomology ' professes to treat, are animals which possess 

 an external skeleton, which are provided with four wings 

 and six legs, which cannot re-produce an injured limb, 

 and finally, which arrive at perfection by undergoing meta- 

 morphosis in one or other of the following modes. 



1. By passing through an amorphous state, — 



AMORPHA ; 



In which the penultimate state is provided neither with 

 mouth nor organs of locomotion ; consequently it neither 

 eats nor moves, nor does it bear any resemblance to the 

 perfect state. This group contains two classes of insects. 



Class I. Lepidoptera ; in which the perfect insect has 

 four fully developed wings, all of them covered with a 

 kind of scales, which are symmetrically arranged on 

 each other, like the scales of a fish or the tiles of a 

 house. The silk- worm, p. 17, and all moths and 

 butterflies, are examples of this class. 



Class II. DiPTERA ; in which the perfect insect has two 

 fully developed wings, and two merely rudimentary 

 ones, which are distinguished by the name of halteres 



