4 INSECTS : THEIR STRUCTURE AND FOOD. 



and the last ono ov two wl.icl. wo may call tlio tail. Tlieso segments are 

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

 projeetions on which are hooks ; Ihese are sucker-feet and there is a fifth 

 l)aii- on the tail. Each of the eight segments has a small dark spot on each 

 side, and a similar si)ot is found on the thorax ; these s]wts are Higmata,'^ 



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. 



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

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

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

 antenna?, 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 sldn 

 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 cJiitin. 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. 



Fig. 7. 



A Wasp, showing the divisions of the body 



in a winged insect. 



Stigma, a spot ; plural, stigmc^ta, spots. 



