MOTIONS OF INSECTS. $19 
Other insects again leap by means of the abdomen or 
some organs attached to it. An apterous species—be- 
longing to the Ichneumonid@, and to the genus Cryptus, 
F'.—takes long leaps by first bending its abdomen in- 
wards, as De Geer thinks, and then pushing it with 
force along the plane of position?. There is a tribe of 
minute insects amongst the Aptera, found often under 
bark, sometimes on the water, and in various other si- 
tuations, which Linné has named Podura, a term im- 
plying that they have a leg in their tail. This is literally 
the fact. For the tail, or anal extremity, of these insects 
is furnished with an inflexed fork, which, though usually 
bent under the body, they have the power of unbend- 
ing; during which action, the forked spring, pushing 
powerfully against the plane of position, enables the ani- 
mal to leap sometimes two or three inches. What is 
more remarkable, these little animals are by this organ 
even empowered to leap upon water. ‘There is a minute 
black species (P. aquatica, L.) which in the spring is 
often seen floating on that contained in ruts, hollows, or 
even ditches, and in such infinite numbers as to resem- 
ble gunpowder strewed upon the surface. When dis- 
turbed, these black grains are seen to skip about as if 
ignited, jumping with as much ease as if the fluid were 
a solid plane, that resists their pressure. The insects 
of another genus—separated from Podura by Latreille 
under the name of Smznthurus—have also an anal spring, 
which when bent under the body nearly reaches the 
head. These, which are of a more globose form than 
Podura, are so excessively agile that it is almost impos- 
sible to take them. Pressing their spring against the 
aa 10: b PraTtE XV, Fic, 10. 
