3 86 GENERAL SCIENCE 



The life history of an insect is very interesting for 

 observation and study. There are four principal stages 

 through which the insect passes. First, the egg stage; 

 second, the larva stage or eating period; third, the pupa 

 stage; fourth, the adult stage. During the pupa stage 

 the insect changes its body from the worm-like form to 

 that of the adult. In the adult stage the insect has six 

 legs, usually two pairs of wings, and some have a pro- 

 boscis for eating liquid foods, while some do not eat at all 



in the adult stage. The insects 

 which do not eat during the adult 

 stage live only a week or so. Flies, 

 mosquitoes, and some butterflies 

 which eat liquid foods may live 

 for months or even over the winter 

 in the adult stage. 



267. Crayfish. Crayfish are 

 very common and can be found 

 in creeks and in holes in the 

 ground, ranging from low swampy 

 ground to the hilltops. Their 

 principal use to man is as scav- 

 engers, that is, they devour quantities of decaying ani- 

 mal matter in the creeks or about the holes which they 

 make in the ground. 



The body of the crayfish is covered with a bony-like 

 shell, an exoskeleton, which serves to protect it from its 

 enemies. It can swim backward very rapidly by swift 

 motions of its tail, which is composed of several flat bony- 

 like parts. It has two stalked compound eyes which 

 enable it to see in all directions, and it is thus able to 

 escape its enemies. It has five pairs of legs, all of which 

 are attached to the thorax. The four back pairs are used 



