STRUCTURE OF INSECTS. 377 



only from the beauty of their structure, and the nicety 

 with which they are adapted to the other habits of the 

 animal ; but as they are a very convenient means of 

 classing the animals. 



Most winged insects have four wings, though in all, 

 the four are not of similar structure, or equally deve- 

 loped. The wings, which are the proper organs of 

 flight, are constructed of a delicate network, of the 

 horny substance which has been alluded to, upon which 

 is spread a thin membrane of the same. Frequently 

 those membranous wings are covered over with fea- 

 thers or scales, which also sometimes, as in the sphinx- 

 moths, cover other parts of the insect. 



The two upper wings are often horny and not adapt- 

 ed for flying, but they serve as a protection to the 

 others. These are the elytra ; and the insects which 

 have them, beetles, as they are indiscriminately called 

 in common language, are in the habit of creeping into 

 places where membranous wings would be in danger 

 of being torn ; or diving in water, where they would be 

 rendered unfit for the purposes of flight. Even the 

 membranous wings of insects, however strong in every 

 thing but the scales with which some of them are co- 

 vered, are much less liable to injury than one not ac- 

 quainted with them would be apt to imagine. 



Sometimes the upper wings are only half the length, 

 and adhere to the membranous ones that are below ; 

 and in many, the two under wings are not developed, 

 but form a slender stalk behind each wing, ending in a 

 knob. These organs are called halter es or balancers. 

 It is doubtful, however, whether these ought, in all 

 cases, to be considered as the rudiments of the second 



