342 THE MECHANICAL FUNCTIONS. 



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-talpa> or mole cricket, presents 

 a remarkable example. A minute account of the 

 anatomy of this insect has been given by Dr. 

 Kidd,* from which it appears that being des- 

 tined, 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 pe- 

 culiarly calculated for burrowing, with a skin 

 which, being covered with a fine down, effec- 

 tually prevents the adhesion of the moist earth 

 through which it moves ; and with a form of 

 body enabling it to penetrate with least resist- 

 ance the opposing medium. By being en- 

 dowed with the power of moving as easily in a 

 backward as in a forward direction, it is enabled 

 quickly to retreat in the narrow channel it has 

 excavated : and as a safeguard in these retro - 



* Phil. Trans, for 1825, p. 203. 



