PROGRESSIVE MOTION OP INSECTS. 241 



with a peculiar mechanism for the special purpose of accom- 

 plishing a singular mode of leaping, independently of any 

 action of the legs. The legs of this insect are so short, that 

 when it is laid on its back, it cannot turn itself, beino- unable 

 to reach with its feet the plane on which it is lying, and 

 procure a fulcrum for the action of its muscles. It is appa- 

 rently with the design of remedying this inconvenience, 

 that nature has bestowed on this tribe of insects the faculty 

 of springing into the air, and making a somerset, so as to 

 light upon the feet; an effect which is accomplished by 

 an exceedingly curious mechanism. The prothorax is pro- 

 longed beyond the length it usually lias in other coleop- 

 tera, and it is articulated with the mesothofax on the 

 dorsal side by two lateral tubercles, which form a hino-e 

 joint, limiting its motions to a vertical plane. The sternum, 

 or pectoral portion of the prothorax is also extended back- 

 wards, and terminates in an elastic spine, which is received 

 into a cavity in the mesothorax, and which, while the insect 

 is lying on its back, with the prothorax bent upon the meso- 

 thorax, recoils with the force of a spring, and communicates 

 to the body an impulse which carries it upwards to a consi- 

 derable height. If the elater should fail in its first attempts 

 to recover its feet, it repeats its leaps till it succeeds. We 

 find no example of a similar structure in any other part of 

 the animal kingdom. 



The express adaptation of structure to the mode of life 

 designed for each species of insect is nowhere more strongly 

 marked than in those which are intended to burrow in the 

 earth: and of these the Gryllo-ia/pa, or mole cricket, pre- 

 sents a remarkable example. A minute account of the ana- 

 tomy of this insect has been given by Dr. Kidd," from 

 which it appears that being destined, like the mole, to live 

 beneath the surface of the earth, and to excavate for itself a 

 passage through the soil, it is furnished with limbs peculiar- 

 ly calculated for burrowing, with a skin which, being co- 

 vered with a fine down, effectually prevents the adhesion of 



• Phil. Trans, for 1825, p. 203. 

 Vol. I. 31 



