134 



EVOLUTION AND ANIMAL LIFE 



Fig. 75. — Diagram showing variations in elytral pattern of the California 

 flower beetle, Diahrotica soror. (After Kellogg and Bell.) 



to show the spines. In eighty-nine individuals of this' species 

 of locust collected at Ithaca, N. Y., the number of spines in the 



outer row of the right tibiae 



Ac 



varies from nine to fifteen, 

 in the inner row from eleven 

 to sixteen. One not giA^en to 

 the systematic study of insects 

 may think spines on the hind 

 legs very trivial structures in- 

 deed; but the entomologist; 

 using exactly such character- 

 istics as the number of these 

 structures as a means in help- 

 ing him to distinguish and 

 define his species, knows how 

 considerable this variation 

 really is. 



The dog-days cicada (Fig. 



79) also has spines on its hind 



tibiae, but only a few, usually, 



indeed, two. But in any series 



of individuals of this insect some individuals will be found with 



but a single spine, some with three, and a few with four even, 



although the very great majority will have two. For example, 



Fig. 76. — Diagram showing variation in 

 pattern in the yellow jacket, Vespa ger- 

 manica. (After Kellogg and Bell.) 



