SALTATORIAL POWERS OF INSECTS. 289 



forward in the water whereby they are able to dart, from a 

 considerable distance upon their prey. The manner in which 

 this motion is effected is very remarkable, and is possessed by 

 no other insects ; diving in the water and performing respiration 

 without ascending to the surface for fresh supplies of air, these 

 larvas are furnished with an apparatus, whereby they are able 

 to extract oxygen from the water in which they reside. This 

 consists of five plates, affixed at the extremity of the abdomen, 

 which are capable of opening and shutting, so as to enclose 

 within the hollow portion of the abdomen, a quantity of water, 

 which, after it has parted with its oxygen, by the action of 

 various internal organs, is forcibly expelled through the same 

 orifice, by which means the insect is suddenly propelled forward. 



In the click-beetles ( Elateridce) this leap is produced by 

 the sudden jerk given to the body when the insect is laid upon 

 its back, by forcibly striking the acute spine of the breast into 

 the corresponding cavity in front of the mesosternum. 



In other insects, as the ground-fleas (Podurklce), the spring 

 is produced by the sudden unfolding or striking backward of 

 a forked appendage, fixed beneath the extremity of the body. 



It is, however, to the peculiar construction of their legs that 

 insects are, for the most part, indebted for their saltatorial 

 powers. 



Of these the tormenting flea is the most notable example. 

 Furnished with thighs of great muscular power, and clothed in 

 a tough and highly-polished cuirass, no wonder that it effects 

 an escape in almost every situation, and, to use the words of a 

 favourite French author, " Conime Vamour rit en siorete de la 

 hlessure qtielle afaite et de la colere quelle occasioned 



The grasshoppers, locusts, crickets, garden-fleas (Haltic<B, 

 amongst which the destructive turnip-fly is found), and flea- 

 weevils (Orchestes) may be mentioned as examples of leaping 

 powers, originating in the peculiar structure of the hind legs, 

 the thighs being greatly thickened, so as to give support to the 

 powerful muscles wherewith the motion is produced. 



This incrassation of the legs does not, however, necessarily 

 imply the power to leap, since many insects, having very thick 

 hind legs, are only able to walk, and that but clumsily, as 

 though the greatly disproportionate size of their limbs were a 

 hindrance to their motion. Thus, although the hind legs of 

 such exotic species as Bruchus, Bactris, Leucospis dorsiger, 



NO. III. VOL. I. P P 



