PARTS OF INSECTS, AND MISCELLANEOUS OBJECTS. 



121 



thus facilitate its rapid motion. When the wing closes, the insect first turns back 

 the marginal part, and then closes the ribs in the manner of a fan, folding up, 

 within a small compass, the entire delicate structure of the wing, under the pro- 

 tection of the strong shield of the wing-cover. 



Fig. 193. 



The wing-cases are not in all instances composed of a horny substance ; since 

 among the beetle tribe they frequently consist of a softer material like leather. 



When the insect is preparing to fly, the wing-cases are opened to such an ex- 

 tent as to allow full play to the wings ; the insect then launches into the air, 

 striking it vertically with these delicate organs, while the wing-cases are kept im- 

 moveable during the whole time of flight. The resistance presented to the atmos- 

 phere by the latter is supposed to facilitate in some way the motions of these lit- 

 tle beings. The bodies of insects, like the beetle, are almost in an upright posi- 

 tion, during their flight, and present a singular appearance, in the case of the 

 larger kinds, as they move heavily and laboriously along. The wings of the 

 beetle are for the most part of great extent, and the ribs that ramify all over their 

 surface are stronger than those which are found in the wings of other orders of 

 insects ; and are so arranged as to strengthen and support every part. In addi- 

 tion to what has already been remarked regarding the structure of the wings of 

 insects, it may be further observed, that the ribs are hollow tubes originating in 

 the trunk, and that within them are tubular vessels, which are supposed to be 

 air-vessels communicating with the organs of respiration in the trunk. 



