108 



INSECTS DIAGRAM 6. 



O (f^N^ ^,-v 



Portion of Insect's Eye, 

 magnified. 



have 



as in the dragonflies. If we closely examine the eyes of a crab, 

 we see that this convex eye has the appearance of a sieve with 

 a quantity of little holes. Each of these little holes is really an 



eye, and all the articulata, insects 

 as well as others, have, consequently, 

 instead of one eye on each side of 

 the head, two clusters of eyes, each of 

 which is too small in many cases to 

 be distinguished without a magnifying 

 glass. 



The thorax bears the legs and 

 wings. Insects have always six legs. 

 Spiders have eight legs, and form a 

 separate class ; most of the Crustacea 

 ten ; others more or less ; some myriapods have often a 

 considerable number. All insects do 

 not fly; many, like fleas, lice, and 

 chigoes have no wings. Others have 

 only two wings, as the flies. Others 

 again have four. Among the last, 

 there are some in which the four 

 wings are alike, like butterflies, 

 dragonflies, and wasps; but there 

 are other four-winged insects in 

 which the two forewings sometimes 

 differ much from the hind wings, as in the 

 cockchafers and grasshoppers. In this case, the 

 first pair of wings is called the elytra. 



The thorax is chiefly filled by the muscles which 

 move the wings and legs. The digestive organs 

 are in the abdomen. Insects have special organs 

 for respiration, which are also found in spiders, 

 but which are neither lungs nor gills. When the 

 Woodlouse. wings of a cockchafer, for instance, are lifted up, 

 we discover a small imprint on each segment of the abdomen, 



Spider. 



