COLORATION IN POLISTES. 43 



creamy flesh color until the pupal skin is cast and the young imago 

 dries out preparatory to leaving its cell. The yellow then appears 

 uniformly over these areas and gradually deepens to the adult color. 



The pigmentation of the ventral side of the abdomen does not quite 

 keep pace with that of the dorsal. Here, as on the dorsal side, the 

 pigment first appears at the anterior edge of the segment, but the lat- 

 eral spots are larger than on the dorsal side, and pigmentation proceeds 

 more by the centrifugal spreading from these spots than by a posterior 

 spreading from the anterior zones. Plate II, fig. 28, illustrates the 

 condition of the ventral side in a stage already shown for the dorsal 

 side in Plate II, fig. 24. Plate II, fig. 29 represents the corresponding 

 condition in the male. 



On the head the coloration of the vertex and front keeps pace with 

 that of the mesothorax. The first indication is in the form of a spot 

 in the region of the ocelli (PI. II, fig. 19). In the male the face re- 

 mains uniformly flesh-colored until pigmented with yellow. In the 

 .female the clypeus shows a faint central stain at first, and this may 

 spread until the whole surface is darkened. 



The appendages remain unpigmented even after the definite pattern 

 of the body has been clearly indicated. Color first appears here as 

 faint stains near the articulations. Next, brownish lines appear wher- 

 ever the pigmentation is to be deepest in the adult, and from these 

 regions there is a lateral spreading until the permanent color pattern 

 is attained. 



In the zones where individual variation occurs we find the suffusion 

 last to appear. For instance, in the metathorax of specimens whose 

 markings are reduced to two we find the regions where the yellow 

 lateral stripes usually occur to be the last to show pigmentation. The 

 same is true in the case of the lateral spot of the second abdominal 

 segment. This area is sometimes pigmented, and when it is, it is the 

 very last to become so. The pigmentation is brought about by the 

 spread of the pigment posteriorly from the original triangle and ante- 

 riorly from the transverse zone until these two areas come together in 

 the middle zone of the segment. There is then a centripetal spread 

 until the area is wholly suffused. 



DEVE1.0PMENT OF THE Pattern in Poustes paIvLtpes. 



In the dark variety of P. pallipes characteristic of New England, the 

 early developmental stages, as studied in a great many specimens, are 

 identical with those described for P. variatus. The only difference 

 between the two species is that the typical P. variatus stops, so to 

 speak, at an earlier stage than does P. pallipes, which advances to the 



