454 MOTIONS OF INSECTS. 
metathorax, by which motion the mucro is quite liberated from its sheath , 
and then bending them in a contrary direction, the mucro enters it again, 
and the former attitude being briskly and suddenly resumed, the mucro 
flies out with a spring, and the insect: rising, sometimes an inch or two in 
the air, regains its legs and moves off, The upper part of the body, by its 
pressure against the plane of position, assists this motion, during which the 
legs are kept close to its underside, Cuvier, when he says that man and 
birds are the only animals that can leap vertically}, seems to, have forgotten 
the leap of Elaters, which is generally vertical, the trunk being vertically 
above the organ that produces the leap. 
Other insects again leap by means of the abdomen or some organs 
attached to it. An apterous species, belonging to the Ichneumonidae, 
and to the genus Cryptus, takes long leaps by first bending its abdomen 
inwards, as De Geer thinks, and then pushing it with force along the 
plane of position. There is a tribe of minute insects amongst the Apiera, 
found often under bark, sometimes on the water, and in various other 
situations, which Linné has named Podura, a term implying 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 unbending; 
during which, action, the forked spring, pushing powerfully. against the 
plane of position, enables the animal 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), which in the spring is often seen floating on that contained 
in ruts, hollows, or even ditches, and in such infinite numbers as to resemble 
gunpowder strewed upon the surface. When disturbed, these black grains are 
seen to skip about as if ignited, jumping with as much ease as if the fluid 
were asolid plane, that resists their pressure. The insects of another genus, 
separated from Podura by Latreille under the name of Sminthurus, 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 impossible to take them. , Pressing their spring 
against the surface on which they stand, and unbending it with force, they 
are out of your reach before your finger can come near them. One of 
them, SS. fuscus, besides the caudal fork, has a very singular organ, the use 
of which is to prevent it from falling from a perpendicular surface, on which 
they are often found at a great height from the ground. Between the ends 
of the fork there is an elevated cylinder or tube, from which the animal, 
when necessary, can protrude two long, filiform, flexible, transparent threads 
coyered with a slimy, secretion. By these, when it has lost its hold, it 
adheres to the surface on which it is stationed. Another insect related 
to the common sugar-louse, and.called by Latreille Machilis polypoda, in 
some places common under stones 4, has eiglit pair of springs, ane on each 
ventral segment of the abdomen, by means of which it leaps to a won- 
derful distance, and with the greatest agility. 
Climbing is another motion of insects that merits particular considera 
tion ; since, as this includes their power of moying against gravity —as we 
1 Anat, Comp. i. 498, 2 ii. 910. 
5 De Geer, vii. 38. t. iii. f. 10. 7 7. 
4 ‘Lhis insect abounds at Last Farleigh, near Maidstone. 
