WHAT KINDS OF THINGS ARE LIVING? 



15 



10. A representative insect — the grasshopper {Acridium, 

 Melanoplus, Caloptenus, or some other genus). If we examine 

 a grasshopper, we find the general plan of structure to be that 

 of a main body with several kinds 

 of outgrowths. The body has three 

 easily distinguished regions : the 

 head, the thorax, and the abdomen. 



The head bears two feelers, or 

 antennae (singular, antenna), pro- 

 jecting forward, and the eyes oc- 

 cupy a large part of the surface. 

 These large eyes are called com- 

 pound, because each consists of nu- 

 merous complete eyes (see Fig. 6). 

 In addition there are three tiny 

 simple eyes on the front of the 

 head. The mouth occupies the end 

 of the head which is toward the 

 ground when the animal stands in 

 the normal position, and it consists 

 of several distinct parts. 



The thorax, which is covered by 

 the wings when the animal is at 

 rest, is made up of three more or 

 less distinct segments, or rings. 

 Each of these carries one pair of 

 jointed legs. Two of the segments 

 carry one pair of wings each, and 

 the anterior (forward) wings cover 

 the posterior ones when at rest. 



Coming to the abdomen, we 

 find that this too is segmented. 

 Indeed, in the whole class of ani- 

 mals called Insects the body is cut up, or segmented, like the 

 body of an earthworm. On the side of each segment there is a 

 tiny spiracle, or breathing hole (see Fig. 7). The foremost seg- 



Fig. 6. Compound eye 



In the Arthropoda, or jointed-leggea 

 animals, there are compound eyes 

 as well as simple ones. A, head of 

 a locust, showing the compound eye 

 with its many facets, each repre- 

 senting the exposed surface of an 

 ommatidium, or single eye. B, an 

 ommatidium, seen in section cut 

 lengthwise, a, corneal lens; b, lens- 

 growing cells; c, cone; d, iris cells; 

 e, retinal cells, receiving light im- 

 pressions; /, retinal pigment; g, 

 perforated supporting membrane 



