[ 474 1 54 



forms a kind of wall behind the mouth, usually deeply notched in the 

 middle, and which is called the mentum, or chin. 



When the labium forms a narrow elongated piece, distinct from the 

 mentum, as in most of the Coleoptera, it is now generally called the 

 tongne, lingua or Ugula. 



The Falpi, or appendages of the mouth. — Near the base of each max- 

 illa, on its outer side, is attached a moveable appendage, usually' com- 

 posed of four or five joints, and never more than six, called the maxil- 

 lary palpus ; and near the base of the labium is attached a similar pair 

 of organs, but with a less number of joints, distinguished as the labial 

 palpi. These appendages are subject to considerable variation, espe- 

 cially in the shape of their terminal joints, and are made much use of 

 in determining the families und genera of insects. 



The haustellate or suctorial mouth consists of a more or less elongated 

 IDroboscis or sucker, whicli is sometimes short and fleshy, as in the flies, 

 {Muscidae ;) sometimes more elongate, horny antl pointed, as in the 

 bugs, [Hcmiptera ;) and sometimes very long and slender, and rolled 

 up, when not in use, in a spiral coil, as in the buttertiies and moths, 

 {Lepido][)tera.) 



It is evident that all inset'ts with a suctorial mouth must live exclu- 

 sively upon li<piid food, or the juices of animals and plants. 



The kaustollum or sucker is not a single organ, as it appears, but has 

 upon its upper side a deep groove, in which are contained usually either 

 two or four, but in some of the carnivorous species (mos<iuitoes and 

 horse-flies) six needle-shaped loieces, which in these last make a compli- 

 cated weapon with which they pierce the sldns of animals uj^on whose 

 blood they subsist. 



From a comparison of the haustellate with the mandibulate mouth, in 

 different kind of insects, it has been concluded that the apparent sucker, 

 which, as we have just seen, forms a sheath for the smaller needle- 

 shaped i)ieces, corresponds to the labium, and that the contained pieces 

 must represent the mandibles and maxillae, and, where six pieces are 

 present, also the lab rum and lingua. In accordance with the propor- 

 tionately great development of the labium, we find that its appendages, 

 that is, the labial palpi, are also very prominent, whilst the maxillary 

 palpi are very small or rudimental. This is the case in two of the suc- 

 torial orders, the Lepidoptera and Diptera ; but the other order (He- 

 miptera) is excei)tional in this respect, having neither maxillary nor 

 labial palpi developed. 



THE THORAX AND ITS APPENDAGES. 



The thorax is the second, or middle division of the bodies of insects. 

 Though apparently single, it is really composed of three pieces solderedf 



