$16 MOTIONS OF INSECTS. 
the legs are unbended. This insect, when about to leap, 
places its posterior thighs in a direction perpendicular to 
the plane of position, keeping them close to the body; 
it next with great violence pushes them out backwards, 
so as to stretch the leg in a right line. These spines 
then lay hold of the surface, and by their pressure en- 
able the body to spring forwards, when, being assisted 
by its wings, it will make astonishing leaps, sometimes 
as much as five or six feet, which is more than 250 
times its own length; or as if a man of ordinary stature 
should be able at once to vault through the air to the 
distance of a quarter of a mile. Upon glass, where the 
spines are of no use, the insect cannot leap more than 
six inches*.—The species of another genus of this order 
(Chermes, L.), that jamp very nimbly by pushing out 
their shanks, are perhaps assisted in this motion by a 
remarkable horn looking towards the anus, which arms 
their posterior hip.—Some bugs that leap well, Lygaus 
saitatorius, F., &c., seem to have no particular apparatus 
to assist them, except that their posterior tibiae are very 
long.—Several of the minute ichneumons also jump with 
great agility, but by what means I am unable to say.— 
There is a tribe of spiders, not spmners, that leap even 
sideways upon their prey. One of these (Aranea sce- 
nica, L., Salticus, Latr., Attus, Walck.), when about to 
do this, elevates itself upon its legs, and lifting its head 
seems to survey the spot before it jumps. When these 
insects spy a small gnat or fly upon a wall, they creep 
very gently towards it with short steps, till they come 
within a convenient distance, when they spring upon it 
@De Geer, ii. 178. 
