MOTIONS OF INSECTS. 489 



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 oft'. 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 Ichneumonida, and 

 to the genus Cry plus, 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 

 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 Sminthwus, 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, S.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 

 hei"[ht 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 lonw, filiform, flexible transparent threads covered with a slimy secre- 

 tion. 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 MachiUs pofypoda, in some places common under 

 stones^, has eight pair of springs, one on each ventral segment of the 

 abdomen, by means of which it leaps to a wonderful distance, and with 

 the greatest agility. 



> Annt. Comp. i. 498. » ii. 910. 



» De Geer, vii. 38. t. iii. f. 10. r r. 



* This insect abounds at East Farleigh, near Maidstone. 



