PROGRESSIVE MOTION OF INSECTS. 305 



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

 and procure a fulcrum for the action of its muscles. 

 It is apparently 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 on the feet ; 

 an effect which is accomplished by an exceedingly 

 curious mechanism. The prothorax is articulated 

 with the mesothorax, on the dorsal side, by two 

 lateral tubercles, which form a hinge joint, limiting 

 its motions to a vertical plane. The prosternum, 

 or pectoral portion of the prothorax, is also extended 

 backwards, and terminates in an elastic spine, 

 which is received into a cavity in the mesothorax. 

 While the insect is lying on its back, with the pro- 

 thorax bent backwards on the mesothorax, so as to 

 form together with the head and abdomen a kind 

 of arch, convex upwards, and the spine brought 

 forwards out of its socket, the muscles which tend 

 to bring these two segments of the thorax into a 

 straight line are thrown into strong action, and the 

 prothorax, together with the base of the elytra, are 

 made to strike with violence against the plane on 

 which the insect is lying: the force of the blow 

 being augmented by the sudden re-entrance of the 

 spine into its socket, with the eftect of a spring. The 

 elater is thrown upwards by the reaction of the 

 plane of support : but as the impulse is given to it 

 at a point anterior to the centre of gravity, a rota- 

 tory force is communicated, by which the body, 

 while in the air, is turned over, and falls with its 

 feet on the ground. It retains itself in this position 

 by suddenly clinging with its legs extended, and 

 thus guards against a rebound, which might again 



VOL. 1. X 



