452 PHYSIOLOGY. 



body. The following genera of minute Colecpterrt, Hi/mencptern, and 

 Hemiptera class themselves with it in this power of leaping, and we 

 place them in the order of the progressive decrease of the function ; for 

 instance, Haltica, Orchestes, Eupelmus, Chalcis, and other Ptero- 

 malidce, Jassus, Aphrophor,a, Chermes, Livia, &c. The larger Cicada, 

 grasshoppers, and locusts do not leap so well. We also find a few 

 minute Diptera possessing this power ; for instance, many species of 

 the genera Ceratopagon and Tachydromia, in the first the males espe- 

 cially, but in general their activity is but small, which is probably 

 occasioned by their softer integuments, whence the contraction of the 

 muscles is much less, but which also may be partly ascribed to the less 

 perfect development of the muscles themselves. 



The two families of insects in which we detect peculiar organs for 

 leaping are the Elaters and the spring-tails (Podnra, Smynthurus, &c.) 

 In Elater, the articulation of the pro- and meso-thorax gives them 

 the power of leaping, but it can only be accomplished when the insect 

 lies upon its back, whence, should it by any accident be placed in this 

 position, it could not readily recover itself, owing to its short legs and 

 flat back ; nature has therefore supplied it with assistance in the mode 

 of the articulation of the two thoracic segments. For this purpose the 

 mesonotum and mesosternum are prolonged into a projecting tubular 

 process, which is fitted to a cavity in the pronotum and prosternum ; 

 upon this process we find in the middle of the anterior margin of the 

 mesonotum a hook-shaped joint, bent upwards, adapted to a cavity in 

 the posterior margin of the pronotum. At the base, close to this'hook, 

 there are two smooth flat articulations, which likewise fit two flat 

 cavities in the pronotum. The mesosternum has, on the contrary, 

 exactly in its centre, a deep funnel-shaped groove, into which a conical 

 process of the prosternum fits ; upon the anterior margin, close to this 

 large groove, there are two smaller cavities for the reception of two flat 

 processes, which lie at the base, close to the conical process of the pro- 

 sternum. Their connexion is effected by a tubular membrane, which 

 passes from one segment to the other. If now the insect lie upon its 

 back, by means of the muscles which connect the two dorsal plates 

 together it raises its body upwards, so that the pronotum, moving upon 

 the processes of the mesonotum, bends back upon the dorsal surface of 

 the body. It now suddenly contracts with all its force the connecting 

 muscles of the two thoracic segments, as well as the others which run 

 down from the mesonotum to the prosternum, and it thereby strikes 



