12 INSECTS IN G-ENERAX, 



forms a kind of wall belihul the mouth, usually deeply uotehed iu the 

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



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

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

 tongue, lingua or Ik/nla. 



The Falpi, or appendages of the mouth. — '^ear the base of each max- 

 illa, on its outer side, is attached a movable 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 and genera of insects. 



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

 proboscis or sucker, which is sometimes short and fleshy, as in the flies, 

 {MuseUJcc ;) someritues more elongate, horny and pointed, as in the 

 bugs, {Ileiniptera ;) and sometimes very loug and slender, and rolled 

 up, when not in use, iu a spual coil, as in the butterflies and moths, 

 [Lepidoptera.) 



it is evident that all insects with a suctorial mouth must live exclu- 

 sively upon liquid loud, or the juices of animals and plants. 



The hauHtclluiii 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 (mosquitoes and 

 horse-flies) six needle sliaped i)ieces, which iu these last make a compli- 

 cated weapon with which they pierce the skins of animals upon whose 

 blood they subsist. 



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

 diflerent kinds of insects, it has been concluded that the apparent sucker, 

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

 shaped pieces, corresponds to the labium, and that the contained pieces 

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

 present, also the labrum and lingua. In accordance with the i)ropor- 

 tionately great develoi)ment of the labium, we find that its ap])endages, 

 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 (Hemip- 

 tera) is exceptional 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 soldered 



