120 



Species and Species Change 



pennsylva nica • 



(Fall Brood) 



mo 



pennsylvanica o 



(Spring Brood) 



rubens » 



14 15 16 



17 18 19 20 21 22 23 24 25 26 27 



BODY LENGTH IN MM. 



Fig. 46. Differences in body proportions between genetically distinct species 

 of field crickets of the genus Acheta (oviods fitted by eye). To date these are 

 the best morphological criteria for the separation of these species. (Modified 

 from R. D. Alexander.) 



