PROGRESSIVE MOTION OF INSECTS. 341 



quarter of a mile. When the same insect is laid 

 on glass, on which the spines cannot fasten, it is 

 unable to leap farther than six inches.* 



The insects belonging to the genus Elater 

 are provided with a peculiar mechanism for the 

 special purpose of accomplishing 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, being 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 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 upon the feet ; an effect 

 which is accomplished by an exceedingly curious 

 mechanism. The prothorax is prolonged beyond 

 the length it usually has in other coleoptera, and 

 it 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 sternum, 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, and which, while the insect 

 is lying on its back, with the prothorax bent 

 upon the mesothorax, recoils with the force of 



* De Geer, III. 178, quoted by Kirby and Spence, 



