MOTIONS OF INSECTS. 349 



the four ordinary ones, it has a winglet {Alula) attached 

 to the base of the lower one, and placed, when the wings 

 are folded, between it and the npper. These organs in 

 this order you know are covered with scales of various 

 shapes \ Their nervures are diverging rays, which issue 

 either from a basal area or from the base itself, and 

 terminate in the exterior margin''. The wings of many 

 male butterflies, hawk-moths, and moths, are distin- 

 guished by a remarkable apparatus, noticed by De Geer, 

 and since by many other naturalists '^ for keeping them 

 steady and underanged in their flight. The upper 

 wings, on their underside near their base, have a minute 

 process, bent into a hook [Hamus), and covered with 

 hairs and scales. In this hook one or more bristles 

 {Tendo), attached to the base of the under wing, have 

 their play. When the fly unfolds its wings, the hook 

 does not quit its hold of the bristle, which moves to and 

 fro in it as they expand or close. The females, which 

 seldom fly far, often have the bristles but never the 

 hook. The hairy tails of some insects, Sesia, belongmg 

 to the hawk-moth tribe, are expanded when they fly, 

 so as to form a kind ot" rudder, which enables them to 

 steer their course with more certainty. 



The insects of this, and of every other order, except 

 the Coleoptera, fly with their bodies in a horizontal posi- 

 tion, or nearly so. As their wings are usually so ample, 

 we need not wonder that the Lejndoptera are excellent 

 fliers. Indeed they seem to flit untired from flower to 

 flower, and from field to field ; impelled at one while by 

 hunger, and at another by love or maternal solicitude. 



■■ Plate XXII. Fig. 7—. '' Platk X. Fig. G. 



' De Geer, i. 173. t. x.f. 4. Linn. Tram, i, 1.35-. 



