INSECTS 



head, a thorax bearing the legs, and a terminal abdomen 

 (Fig. 63). On the head is located a pair of long, slender 

 antennae {Ant) and a pair of large eyes (E). Winged in- 

 sects have usually two pairs of wings attached to the back 

 of the thorax {Wi, JV 3 ). 



The outside of the insect's body, instead of presenting a 

 continuous surface like that of most animals, shows many 

 encircling rings where the hard integument appears to be 

 infolded, as it really is, dividing each body region except 

 the head into a series of short overlapping sections. These 



body sections are called 

 segments, and all insects 

 and their relatives, in- 

 cluding the centipedes, 

 the shrimps, lobsters, and 

 crabs, and the scorpions 

 and spiders, are seg- 

 mented animals. The in- 

 sect's thorax consists of 

 three segments, the first 

 of which carries the first 

 pair of legs, the second 

 the middle pair of legs, and the third the hind pair of legs. 

 The abdomen usually consists of ten or eleven segments, 

 but generally has no appendages, except a pair of small 

 peglike organs at the end known as the cerci, and, in the 

 adult female, the prongs of the ovipositor (Fig. 2 B), which 

 belong to the eighth and ninth segments. 



The head, besides carrying the antennae (Fig. 63, Ant), 

 has three pairs of appendages grouped about the mouth, 

 which serve as feeding organs and are known collectively 

 as the mouth parts. The presence of four pairs of append- 

 ages on the head raises the question, then, as to why the 

 head is not segmented like the thorax and the abdomen. 

 At an early stage of embryonic growth the head is seg- 

 mented, and each pair of its appendages is borne by a 

 single segment, but the head segments are later condensed 



[12] 



Fig. 8. A young grasshopper, or nymph, 

 in the second stage after hatching 



