560 PHILOSOPHY OF ZOOLOGV. 



urged against this method is its limited nature, arising 

 from the great increase of sj^ecies, and the consequent influx 

 of new^characters calling for the formation of additional di- 

 visions. ^ 



Fabricius introduced a method of classifying insects, 

 founded on the organs of the mouth, which has met with 

 many admirers. These histrumenta cibaria furnish per- 

 manent and definite characters, and exhibit, in the modifi- 

 cations which they present, marks well calculated for fix- 

 ing the limits of species and genera. They are, however, 

 in many cases minute ; careful dissection is requisite for 

 their display; and not unfrequently the aid of the mi- 

 croscope is necessary. 



These considerations have induced modern entomologists 

 to combine the two systems of LiNNiEUs and Fabricius, 

 and to add that of Swammerdam. The characters em- 

 ployed by LiNN.EUs occupy the first rank, because they 

 are most obvious to the senses. Those of Fabricius are 

 resorted to in cases where the locomotive organs do not fur- 

 nish marks sufficiently characteristic. 



Insects may be divided into two classes, according as the 

 mouth is fitted for cutting hard substances, or sucking 

 fluid matter. 



I.— INSECTA MANDIBULATA. 



This class is usually subdivided into the seven following 

 Orders : 



Order I. — Coleoptera. 



The insects of this order have their integuments of a 

 coriaceous consistence, approaching, in some genera, to the 

 hardness of shell. The vvings are four in number. The 

 upper part, denominated elytra, are of the same texture 

 with the skin. They are convex above, concave below. 



