PHYLUM ARTHROPODA — CLASS INSECTA 



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characteristic features of the insects. Because of their great varia- 

 tion, wings are of much value in classification. The wing is com- 

 posed of a network of thickened lines called veins and thin areas 

 between the veins called cells. The number, arrangement, and char- 

 acter of the veins and cells are an aid in grouping insects into 

 families, genera, and species. The majority of insects possess two 

 pairs of wings ; there are some, however, that have but one pair and 

 some groups are wingless. 



Fig. 17G. — Right wings of a grasshopper. A, the fore wing; B, the hind wing. 

 (From Henderson, permission of Utali Agricultural Experiment Station.) 



Abdomen 



The segments of the abdomen are usually simple, but the number 

 varies greatly in different insects. There are only ten present in 

 many insects, yet in the embryo of the insect there are eleven. The 

 jointed appendages have been almost entirely lost in adult insects. 

 On the eighth and ninth segments of the female and the ninth of 

 the male are paired structures forming the genitalia which are the 

 external organs of reproduction. Within the abdomen are found 

 the respiratory, digestive, and genital systems. 



