134 



EVOLUTION AND ANIMAL LIFE 



FIG. 75. Diagram showing variations in elytral pattern of the California 

 flower beetle, Diabrotica 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 

 varies from nine -to fifteen, 

 in the inner row from eleven 

 to sixteen. One not given 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.) 



