INDIVIDUAL DIFFERENTIATION AND ADAPTATION. 109 



FIG. 51. 



FIG. 51. Galls on oak, cynipid (Holcaspis duricoria). Natural size. Photo by Folsom. 



FIG. 52. 



FIG. 52. Galls on elm, produced by an aphid, Colopha ulmicola. Natural size. 

 Photo by J. W. Folsom. 



