ORDERS OF INSECTS. 163 



one under the name of " beetles." The leading peculiarity of 

 the Coleoptera is to be found in the fact, that though all the 

 four -wings are present, only the posterior pair are mem- 

 branous, and perform the function of wings. The anterior pair 

 of wino-s are no longer capable of being used in flight, but are 

 hardened by the deposition of chitine, and constitute pro- 



FiG. 74. — Coleoptera. The common Cockcliafer (Melolontha vulffarin), with the elytra 

 closed, and in flight. 



tective cases, which cover the hind-wings, and are known as 

 " elytra " (Gr. elutron, a sheath). The mouth in all the beetles 

 is masticatory, and is furnished with biting and chewing jaws. 



The larviE of the beetles are all worm-like grubs, with 

 masticatory mouths, and they all pass through a complete meta- 

 morphosis, generally requiring a protracted period for its com- 

 pletion. The known number of different kinds of beetles can- 

 not be estimated with any certainty, but it is probably little 

 short of 50,000 species, and this estimate has been doubled 

 by some writers. They are, as a general rule, remarkable for 

 their hard, chitinous skin, their glittering, often metallic, 

 colors, and their voracious habits, though many of them feed 

 upon vegetable matters. 



Of the enormous number of known Beetles, the only one 

 which can be said to be of any decided use to man is the so- 

 called " Blister-beetle," or " Spanish Fly " ( Cantharis vesica- 

 toria). This handsome insect is a native of Southern Europe, 

 especially of Italy, Spain, and France, and lives upon the 

 leaves of the ash, lilac, elder, and poplar. It is largely col- 

 lected and exported for medicinal purposes, as it yields one of 

 the most generally used and eflScient of blisters. 



