MOTIONS OF INSECTS. 



255 



from its sheath ; and then bending them in a contrary direc- 

 tion, 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 1 , 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 Ichneumonidce, 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. 2 There 

 is a tribe of minute insects amongst the Aptera, found often 

 under bark, sometimes on the water, and in various other 

 situations, which Linne 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 a solid 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 



1 Anat. Comp. i. 498. 



a ii. 910. 



