12 INSECTS IN GENERAL 



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

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



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

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

 tongue, lingua or Ugula. 



The FaJpi, or appendages of the mouth. — Near 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 shaj)e of their terminal joints, and are made much use of 

 in determining the families and genera of insects. 



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

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

 {2Iuscidw ;) sometimes more elongate, horny and pointed, as in the 

 bugs, [llcmlptera }) and sometimes very long and slender, and rolled 

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

 {Lepidopiera.) 



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

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



The hau.sfellutn or tsucker 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 carniv^orous species (mosquitoes and 

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

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

 blood they subsist. 



From a comparison of the haustellate M'ith the mandibulate mouth, in 

 different kinds of insects, it has been concluded tluit 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 maxilhe, and, where six pieces are 

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

 tionately great development of the labium, we find that its apj)eudages, 

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

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

 torial orders, the Le[»idoptera and Dipteraj but the other order (Ilemip- 

 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 ax^pareutly single, it is really composed of three pieces soldered 



