STUDIES OF VARIATION IN INSECTS 283 



various places on the campus of Stanford University, a consider- 

 able variation in the black patterning on the yellow ground of the 

 dorsal surface of the abdominal segments was noted. The yel- 

 low jackets are insects of complete metamorphosis, the colors 

 and patterns of the adults (imagines) appearing in definitive and 

 unchangeable condition immediately on the expanding and dry- 

 ing of the legs, wings and body-wall, after issuance from the 

 pupal cuticle. The wasps are well-defended insects by reason of 

 their sting, and the conspicuous black and yellow colors in banded 

 pattern are usually looked on as of the nature of warning colors. 

 If so their condition is due in some or large degree to the action 

 of natural selection, and variations in the pattern are to be looked 

 on as advantageous or disadvantageous. 



We have arranged the 496 individuals of the lot into six 

 principal classes based on the variation in the black markings 

 on the dorsum of abdominal segment 2, and inside of these six 

 into ten other classes based on the variations in the black mark- 

 ings on the dorsum of abdominal segment 5. These classes are 

 as follows : 



Class A: 71 individuals with both black spots of segment 2 

 free from anterior black transverse bar (fig. 54, A). Subclass 

 Aa : 40 (of Class A) have the corresponding two spots of seg- 

 ment 5 attached (fig. 54, Aa). Subclass Ab : 8 have both of 

 them free (fig. 54, Ad). Subclass Ac : 3 have the right spot 

 free and the left attached (fig. 54, Ac). Subclass Ad : 2 have 

 the left spot free and the right attached (fig. 54, Ad). (In 18 

 individuals we could not make out the condition on segment 5 

 without breaking up the dried specimens.) 



Class B : 22 individuals with the left spot of segment 2 at- 

 tached and the right one free (fig. 54, I^). Subclass Ba : 13 

 have both the spots of segment 5 attached (fig. 54, Ba). Sub- 

 class Bb : I has both of these spots free (fig. 54, Bd). (In 8 

 individuals we could not make out the condition on segment 5 

 without breaking up the dried specimens.) 



Class C : 7 individuals with the right spot of segment 2 at- 

 tached, the left one free (fig. 54, C). Subclass Ca : 6 have 

 both the spots of segment 5 attached (fig. 54, Ca). Subclass 

 Cb : I has both of these spots free (fig. 54, Cd). 



