COLORATION IN POLISTES. 



23 



Inspection of the corresponding region in the female (fig. 11) shows 

 quite as great a variability of pattern, but the condition is decidedlj' 

 more melanic (d' , c') than for the males possessing a similar pattern on 

 the dorsal surface of the abdomen. In general, the trend toward 

 melanism is marked by transitions similar to those already described 

 for the dorsal surface. The marking of the second segment is more 

 pronounced than in the others, and varies from a yellow-bordered area 

 with yellow lateral spots tinged at the edges with ferruginous, through 

 three series to the maximal melanic condition. On the main trend the 

 lateral spot becomes obscured by ferruginous, this in turn by black, 

 until finally only a slight dark brown spot persists in the posterior 

 angles of the segment, which is narrowly bordered with yellow. On 

 the second trend this area is largely obscured by black, and has a 



Fig. 10.— Condition of males from southeastern 

 Wisconsin, with reference to ventral ab- 

 dominal markings. The innermost circle 

 (a) represents the pattern corresponding 

 mo.st closely with the modal conditions for 

 the dorsum of the abdomen. (See pi. I, 

 figs. 3, 9-14.) 



a, b, d. A series of transitions to the maxi- 

 mal melanic condition. (PI. I, fig. 38.) 



a, b', d'. Series of transitions to a similar con- 

 dition, but through forms showing a de- 

 creasing black spot. 



a. c" . Series of transitions to a maximal 

 xanthic condition. 



a, d" . Transitions to a melanic condition in 

 which the prevailing tone is fuscous. 



From this it will be seen that the ventral 

 side of the male is prevailingly xanthic. 



slight yellow dot in the postero-lateral angle of one or both sides. In 

 the third trend the main body color tends toward a fuscous, and that 

 of the border and spots toward a russet. All three trends unite in a 

 uniform dark-colored form with narrow terminal borders. Only a few 

 specimens represent the xanthic trend toward large lateral spots with 

 prominent borders. Plate I illustrates the condition just described, 

 and text fig. 9 the distribution of material under the various types. 

 These diagrams show, first, the great similarity between the trends of 

 development for the dorsal surface (fig. 7) and those for the ventral sur- 

 face of the male (fig. 10), and, secondly, the marked tendency toward 

 melanism displayed in the ventral surface of the female (fig. 11). The 

 degree of melanism for the ventral surface is always in advance of the 

 dorsal. Examination of individual specimens shows this to be the case ; 



