INTRODUCTION. 



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

 filaments which have received the name of palpi. 



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

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

 parts of 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 con- 

 sists of three segments or rings, 

 the prothorax, the mesothorax, 

 and the metathorax, each of 

 which bears a pair of legs, and 

 they are in general joined to- 

 gether. The wingS are attached Fig. 6. Thorax of Acrocinus longimanus 



to the two posterior segments. 



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

 this rule, though some may not be developed. 



After the segments to which they are attached the legs are 

 called anterior, posterior, and intermediate. The legs are com- 

 posed 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 for example the 

 front leg of a Heterocerus 

 (Fig. 7), and the posterior leg 

 of a Zophosis (Fig. 8), genera 

 of beetles. 



We shall not dwell on the 

 different parts, as they perform 

 functions which will occupy us 

 later, when speaking of the 

 various species of the great 

 class of insects. 



The functions which the 

 legs of insects have to perform consist in walking, swimming, or 

 jumping. 



In walking, says M. Lacordaire, insects move their 



Fig. 7. Hind leg of a 

 Heterocerus. 



. 8. Front leg 

 a Zophosis. 



