14 COLORATION IN POLISTES. 



indented yellow margins (PI. I, fig. 2). Each segment is orna- 

 mented laterally with a spot, which is most prominent in the second 

 segment, varying here in size and form, but inclining to an oval which 

 has its longest axis in the direction of the axis of the body. This 

 spot is irregularly bordered with ferruginous, which merges imper- 

 ceptibly into the darker main body color. The first segment has an 

 L-shaped mark on either side, which is more or less confluent with the 

 borders of the segment, while in the segments following the second the 

 lateral spots are largely ferruginous and elongated from right to left. 



From this prevailing t> pe the markings pass by easy stages on the 

 one hand to a type with the yellow areas large and conspicuous (PI. 

 I, fig. i), and on the other to a type with the yellow and indeed the 

 ferruginous almost wholly obscured by fuscous or black (PI. I, fig. 4). 

 The first series of transitions is figured (fig. 7) in the left-hand sections 

 (b"- , c"), the second series of transitions in the right-hand sections {b' ,c') 

 of the diagram. From Plate I it will be observed (fig. i) that in the 

 maximal xanthic condition the lateral spot? are so large as to be confluent 

 with the posterior borders and almost to unite in the middle line, while 

 in the maximal melanic condition (fig. 4) the yellow is restricted to a 

 narrow terminal border. 



The lower section {a, b, fig. 7) represents what may be regarded 

 as another line of "advance" toward the melanic condition just de- 

 scribed. Starting with the prevailing pattern, we find that certain 

 specimens may be said to have the brown margin of the lateral spot 

 obscured by black until all that is left of this spot is a narrow yellow 

 dot parallel with the margin. In the transition to the final condition 

 this is further reduced to a slight suggestion of a dot on one side. 



Finally, these transitions to a melanic condition are paralleled in a' 

 series illustrated in the upper section of the diagram {b'" , d'\ d'"). 

 Here the prevailing tint is fuscous instead of black and the ornamenta- 

 tion of a duller yellow than that hitherto described. 



In brief, the variation in the abdominal markings of this collection 

 may be regarded as consisting simply in the varying degree of en- 

 croachment of the ferruginous, fuscous, or black cuticular pigment, on 

 the yellow hypodermal areas. 



Distribution of Material Among the Various Types. 



The distribution of material among the various types is graphically 

 represented in fig. 7. As has already been stated, the transitions 

 between one type and another and even between parallel lines of devel- 

 opment are so numerous and minute that it is difficult to slate just 

 what proportion of the specimens falls into the different groups. 



