406 EXTERNAL ANATOMY OF INSECTS. 



incapable ; the lingua is tubular, and particularly developed," 

 and, like the maxillce in the first, and the lips in the second, 

 serve for the imbibition of liquids. Kirby calls this mouth, in 

 common vv^ith those of the fourth, fifth, and seventh classes, 

 j)erfect. In the fourth class, Coleoptera, the labrum, mandi- 

 bular, maxillcB, and labium are distinct and osseous, the 

 Vmgua is generally small, often nearly obsolete ; it frequently 

 appears to be inserted in the labium, but I am inclined to 

 believe it invariably originates farther back within the mouth, 

 and, owing to its tenuity, needs this point of attachment. 

 The Coleoptera both gnaw and swallow solid substances. In 

 the fifth class, Orthopiera, the constituent parts of the mouth 

 are all fully developed and osseous, as in the last class, excepting 

 the lingua, which is larger, more fleshy, and, in one of the 

 orders, somewhat tubular. In the sixth class, Hemiptera, the 

 labrum, mandibulce, maxillce, and labium are again attenuated 

 and elongated, and, with the exception of the labrum, which is 

 free, united and formed into a jointed sucker, of which the 

 lingua occupies (as far as I have been able to ascertain) the 

 centre, and is thence darted out in the manner of a lancet into 

 any substance the juices of which the insect wishes to extract. 

 The insects of this class live entirely by suction. Kirby calls 

 this mouth Promuscidate. Here you will observe I have 

 arrived at a kind of mouth very nearly resembling that with 

 which I commenced. The seventh class, Neuroptera, has 

 no uniform structure of parts, but varies as its contents 

 resemble those of the other classes, consequently, neither 

 to the constituent parts of the mouth nor the variations 

 of the segments of the trunk can be assigned any common 

 character. 



The second segment of an insect is the Prothorax ; it is 

 the most important segment, for its variations, combined with 

 those of the mouth above given, will at once determine to 

 what class an insect belongs ; and here allow me to observe, 

 that the variations in the development of this and the adjoin- 

 ing segments is closely dependent on the functions which the 



* In some of the orders, as the bees, the mandibulce are free and corneous, 

 while the maxillfe are pliable, and unite with the lingua in extracting the nectar 

 of flowers. The mouth in Hymenoptera is so various, that the above definition 

 is of but little value, except as subject to further deiinition and qualitication. 



