INSECTS: THEIR STRUCTURE AND POOD. 



FIG. 7. 



A Wasp, showing the divisions of the lody 

 in a winged Insect. 



and the last one or two which we may call the tail. These segments are 

 nearly alike, but the four in the middle usually have a pair of small 

 projections on which are hooks ; these are sucker-feet and there is a fifth 

 pair on the tail. Each of the eight segments has a small dark spot on each 

 side, and a similar spot is found on the thorax ; these spots are stigmata, 1 



or air openings, which admit 

 air to the system of air tubes 

 inside the caterpillar's body. 

 The hairs or bristles found on 

 the segments and the tail are 

 not scattered haphazard, but 

 arranged in a definite manner. 

 These are the salient points 

 that can be seen in any insect. 

 In all insects the head, the 

 thorax and the abdomen are 

 distinct ; the head always bears 

 the eyes, the mouth and jaws 

 and the feelers (antenna) ; 

 the thorax always bears the 

 legs and the wings and is 

 actually composed of three segments, though we cannot always see 

 the division ; the abdomen bears sucker-feet in some insects only and 

 has a varying number of visible segments in different insects. Stigmata, 

 or air openings, are found in all insects, and usually are arranged as in 

 the caterpillar. 



All insects have a more or less hard covering, which is composed of 

 a substance known as chitin ; this is a nitrogenous material, peculiarly 

 resistant to chemicals, which forms an impervious covering. The legs, 

 antennae, wings and all parts of an insect are covered in it ; the thick 

 hard wings of a beetle, the fine scales of a butterfly and the flexible skin 

 of a caterpillar are largely composed of it. 



Speaking generally, the skeleton of an insect is this outer 

 covering; there are no "bones/' but a few chitinous supports of the 

 internal organs. When an insect is killed and dried the whole body 

 perishes except the chitinous covering, so that a pinned collection 

 only consists of this dried chitin. Such insects as have not a suffi- 

 ciently thick covering must be kept in spirit, so that the internal 

 organs may be preserved in order to maintain the natural form of the 

 insect. 



1 Stigma, a spot ; plural, stigmata, spots. 



