INSECTA. 29 



swimming in a dense medium like water, or for walk- 

 ing upon the solid, resisting bottom or the dry land. 

 The appendages were modified to meet all the require- 

 ments of locomotion under such conditions ; but the 

 more difficult problem must now be considered, of 

 motion in a medium like air, which is itself lighter 

 than the body of any of the higher organisms.^ This 

 motion is effected, in the locust and many other in- 

 sects, by means of two pairs of wings. The first pair 

 (PI. I., Fig. 3, ze/' j Fig. i) are long, narrow, and of 

 a parchment-like texture. They completely cover the 

 second pair when at rest, and are, therefore, frequently 

 called wing-covers. The more flexible second pair of 

 wings (Fig. 3, w" ; Fig. i) are much larger and of more 

 delicate texture than the wing-covers. When at rest 

 they lie folded like a fan. The longitudinal folding 

 and the position of the wings when closed has given the 

 name Orthoptera, meaning " straight-winged," to the 

 order to which the locust belongs (see p. 102). The 

 thickened portions extending through the wings are 

 called veins and veinlets ; the thinner parts between 

 these thickened supports are the cells. The disposition 

 of the veins and veinlets or general plan of each wing 

 should be studied, since these are more or less charac- 

 teristic in each order of insects.- The locust's wing 

 is more or less triangular in form, with three margins, — 



1 Many lower organisms, plants as well as animals, and es- 

 pecially spores and germs, are so minute or lightened by dry- 

 ing, that they float in air in vast numbers, forming a large part 

 of the dust of the atmosphere in many places; but these, of 

 course, are not considered in the above statement. 



2 See Comstock's Infrodiiction to Entomology, 



