EXTERNAL ANATOMY OF INSECTS. 13 



insects, are unavailable as distinctive characters. To Clair- 

 ville has been assigned the merit of distinguishing between 

 these supposed different kinds of mouth. He does not de- 

 serve it. Aristotle remarks, that some insects possessed teeth 

 for devouring every thing, whilst others had only a tongue for 

 sucking liquids.' Fabricius was well aware of the distinction; 

 he placed together the four classes, Coleoptcra, Orthoj)tera, 

 Neuroptera, and Ilymenoplera; and in a separate group, 

 LejndojHera, Ilemiptera, and Dq)tera^ Lamarck applied 

 the distinction to divisions. Clairville named those divisions. 

 Savigny investigated more thoroughly, and proved the dif- 

 ference to be rather apparent than real. Aristotle's was the 

 observation of a true naturalist; that of Fabricius no less so ; 

 Lamarck's was the application of a systematist ; Clairville's 

 the clever and apt idea of a nomenclaturist ; Savigny's the 

 discovery of a philosopher. I have not happened to meet with, 

 in print, a distinctive character by which these supposed groups 

 can be separated. It is a dichotomous one. Like all dicho- 

 tomies, it consists of a positive and a negative. It is this: — 

 in the mandibulate classes the mandibles do, in the haustellate 

 classes the mandibles do not, move horizontally. It has no 

 reference to the possession of mandibles : all insects possess 

 mandibles. The food can never reach the a'S02)/iagiis without 

 passing through an intermediate space. Its passage through 

 this space is by suction ; the space is called the haustellum. 

 The butterfly and the beetle alike possess this haustellum; it 

 varies only in length. Any difficulty in obtaining food, which 

 the bulk of the head and body may occasion, is provided for 

 by nature by an elongation of this hausleUum. When, com- 

 bined with this difficulty, the food is solid, the mouth is placed 

 at the extremity of this haustellum, as in weevils. When the 

 food is liquid, the parts of the mouth itself are elongated, and, 

 united, form the luiustdlum, as in bees and butterflies. The 

 caterpillar eats solid substances ; its mouth is necessarily hard 

 for their mastication : the bulk of its head and body offer no 

 obstruction to its obtaining an aifiple supply of food; the 

 passage to the ossophagus is short. The butterfly subsists on 



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