128 THE DEVELOPMENT OF INSECTS 



be recognizable, but they are hardly ever absent 

 altogether ; for instance, the two fore wings of a 

 beetle are modified into what are called wing 

 cases, and fold over its back, protecting the two 

 hind wings, which are more or less membranous, as 

 are those of a bee. They have not the functions 

 of locomotive organs, and are used in flight as 

 poisers. Again in the case of a fly, the hind 

 wings seem to be absent, but they are con- 

 sidered to be represented by two little pro- 

 jecting organs which look like large headed 

 pins or nails, but which are quite useless for 

 locomotive purposes. 



The organs of the mouth are especially liable 

 to modification, and on these the older authors 

 used to frame their classification. Insects were 

 divided by them, primarily, into two great 

 divisions, viz. those which had a biting and those 

 which had a sucking mouth ; treated in this 

 way, the following orders fall into the division 

 with biting mouths : 



Coleoptem, or beetles ; Hymenoptera, or bees, 

 wasps, ants, etc. ; Orthoptera and Neuroptera, 

 which include the grasshoppers, earwigs, cock- 

 roaches, dragonflies, May flies, etc. 



