288 . MOTIONS OF INSECTS. 
ceous legs: since, however, they are temporary, vanish 
ing altogether when the insect arrives at its perfect state, 
—are merely used, for they do not otherwise assist in 
this motion, as props to hinder its long body, when it 
walks, from trailing on the ground; to push against the 
plane of position ; and, by means of their hooks or claws, 
to fix itself firmly to its station when it feeds or reposes, 
—I shall therefore call them prolegs (propedes). ‘These 
organs consist of three or four folds, and are commonly 
terminated, though not always, by a coronet or semicoro- 
net of very minute crooked claws or hooks. These claws, 
which sometimes amount to nearly a hundred on one 
proleg, are alternately longer and shorter. ‘They are 
crooked at both ends, and are attached tothe proleg by 
the back by means of a membrane, which covers about 
two-thirds of their length, leaving their two extremities 
naked. Of these the upper one is sharp, and the lower 
blunt. The sole, or part of the prolegs within the claws, 
is capable of opening and shutting. When the animal 
walks, that they may not impede its motion, it is shut, 
and the claws are laid flat with their pots inwards; but 
when it wishes to fix itself, the sole is opened, becoming 
of greater diameter than before, and the claws stand 
erect with their points outwards. ‘Thus they can lay 
stronger hold of the plane of position *. 
The number of these prolegs varies in different spe- 
cies and families. In the numerous tribes of saw-flies 
(Tenthredo, L.), the larvae of which resemble those of 
Lepidoptera, and are called by Reaumur spurious cater- 
pillars (fausses chenzlles), one family (Cimbex, Y. Lophy- 
* Lyonet, 82—t. iii. f. 10-16. 
