6 THE INSECT WORLD. 



At first sight there seems no similarity between the mouth of a 

 biting insect and of one living by suction. But on examination it is 

 found that the parts of the mouth in the one are exactly analogous 

 to the same parts in the other, and that they have only modifications 

 suiting them to the different purposes which they have to fulfil. 



The mouth of a biting insect is composed of an upper lip, a pair 

 of mandibles, a pair of jaws, and a lower lip (Fig. 5). 



The lower lip and the jaws carry on the outside certain appendages 

 or filaments which have received the name of palpi. 



When speaking of sucking insects, and in general of the various 



Fig. 5. Mouth of a masticating insect. Fig. 6. Thorax of Acrocinus longimanus (a beetle). 



orders of insects, we shall speak more in detail of the various parts or 

 the mouth. 



The thorax (Fig. 6), the second primary division of the body of 

 insects, plays almost as important a part as the head. It consists of 

 three segments or rings, which are in general joined together the 

 prothorax, the mesothorax, and the metathorax, each of which bears 

 a pair of legs. The wings are attached to the two posterior segments. 



All insects have six true legs. There is no exception whatever 

 to this rule, though some may not be developed. 



From the segments to which they are attached, the legs are called 

 anterior, posterior, and intermediate. The legs are composed of four 

 parts : the trochanter, a short joint which unites the thigh to the 

 body ; the thigh or femur ; the tibia, answering to the shank in 

 animals ; and the tarsus, or foot, composed of a variable number of 

 pieces placed end to end, and called the phalanges. 



We take as examples the hind leg of a Heterocerus (Fig. 7), and the 

 front leg ofiZcptosis (Fig. 8) (genera of beetles). 



