362 ARTICULATES: INSECTS. 



placed along the sides of the body, and connected with a 

 system of air-tubes, called tracheae, which branch through- 

 out the interior of the body and carry air into every part. 

 It includes three orders, Insects proper, Spiders, and 

 Myriapods. 



Insects proper have the body divided into three plainly 

 marked regions, the head, chest or thorax, and hind 

 body or abdomen. The head is furnished with antennae, 

 mouth, and eyes ; to the thorax are appended the legs 

 and wings, when these exist ; and the abdomen contains 

 the principal organs of digestion and other viscera, and 

 to it belong the piercer and sting with which many insects 

 are provided. The antennae serve the purpose of feelers, 

 and are also probably connected with the sense of hear- 

 ing. The mouth-parts are modified in some groups for 

 chewing purposes, in others as sucking organs. The 

 eyes, though apparently only two in number, are really 

 compound, each consisting of many single eyes closely 

 united, and incapable of being moved in their sockets. 

 Many winged insects have one, two, or three eyelets on 

 the crown of the head. The legs are six in number, and 

 are attached to the under side of the thorax, one pair to 

 each of the three rings. The leg consists of the hip-joint, 

 by which the leg is fastened to the body, the thigh, the 

 shank, and the foot, the latter consisting generally of 

 five pieces, called tarsi, connected end to end, and armed 

 at the extremity with one or two claws. The wings are 

 two or four, or wanting. The piercer more properly 

 ovipositor mentioned above, is in some cases a flexible 

 or jointed tube, capable of being thrust out of the end of 

 the body, and is used for conducting eggs into holes where 

 they are to be deposited ; in other cases it consists of a 

 scabbard containing a central borer or saws, which are 

 used in making holes in which eggs are to be placed. 

 The sting a modified ovipositor consists of a sheath 



