STUDIES OF VARIATION IN INSECTS 285 



Class F: 154 individuals with both spots of segment 2 with 

 their attaching stems reduced to mere short broad bars tending to 

 be wider at base (attachment) than at free end (fig. 54, F). All 

 these individuals have both spots of segment 5 attached. 



From this rough grouping it is obvious that the modal, or 

 most usual pattern is one in which both spots of segment 2 and 

 both of segment 5 are attached. From this condition to that in 

 which both are free in both segments, there is a perfectly con- 

 tinuous series of gradations. Indeed the characteristic thing 

 about this case of pattern variation is its perfect exemplification 

 of typical continuous variation, the connecting of its extremes 

 by perfect series of almost insensibly slight gradations. 



The pattern of the frons of the head of another, smaller lot 

 of 238 individuals of the same species of Vespa was examined 

 for variation. The specimens have been divided into four 

 classes as follows : 



Class A : 137 individuals with a single central free spot 



(fig- 55, A). 



Class B : 64 individuals with the spot attached by a narrow 

 stem (fig. 55, ). 



A 



FIG. 55. Diagram showing var. in pattern of frons of the yellow jacket, 

 Vespa sp. 



Class C : 34 individuals with the spot attached by a broad 

 stem so that stem and spot usually form a short broad bar of 

 nearly uniform width (fig. 55, C). 



Class D : 3 individuals with no spot or stem (fig. 55, D). 



Proc. Wash. Acad. Sci., Dec., 1904. 



