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 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 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. fuscusy 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 

 covered with a slimy secretion. By these, when it has lost its hold, it 

 adheres to the surface on which it is stationed. 3 Another insect related 

 to the common sugar-louse, and called by Latreille Machilis polypoda, in 

 some places common under stones 4 , has eight pair of springs, one 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 moving against gravity as we 



i Anat. Comp. i. 498. a ii. 910. 



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



4 This insect abounds at East Farleigh, near Maidstoue. 



