MOTIONS OF INSECTS. 358 
tor besides the four ordinary ones, it has a winglet (dlzia) 
attached to the base of the lower one, and placed, when 
the wings are folded, between it and the upper. These 
organs in this order you know are covered with scales 
of various shape. 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 distinguished 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, 
Sesza, F., belonging to the hawk-moth tribe, are ex- 
panded when they fly, so as to form a kind of 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 
position, or nearly so. As their wings are usually so 
ample, we need not wonder that the Lepidoptera are 
excellent fliers. Indeed they seem to flit untired from 
flower to flower and from field to field; impelled at one 
4 Prate XXII. Fic. 7—. b PraTE X. Fic. 6. 
¢ De Geer, i. 173.4. x. fi 4. Linn. Trans, i. 135—. 
VOL. II. 2A 
