42 COI.ORATION IN POIvISTES. 



ONTOGENESIS OF THE COLOR PATTERN. 



Development of the Pattern in Polistes variatus. 



The pupa is at first of a uniform creamy white color, which, before 

 any trace of the darker pigmentation appears, deepens into a flesh 

 color. About eight days before the emergence of the wasp the first 

 indications of the color pattern appear in the form of dull brown traces 

 on the tegulse. Almost contemporaneously with this there appear three 

 posteriorly converging areas in the mesothorax (PI. II, fig. 19) and 

 two faintly tinted squarish areas in the scutellum. 



The coloration of the mesothorax may now advance until nearly the 

 whole surface is suffused, before pigment appears in any amount over 

 the rest of the body (PI. II, figs. 20, 21.) Next a dark line appears 

 at the base of the post-scutellum, and the metathorax becomes dark- 

 ened at three points. The first of these has the form of a J and is at the 

 anterior end of the median longitudinal groove ; the other two are cir- 

 cular spots at either side of this triangle. At these points the pig- 

 ment gradually deepens and then spreads posteriorly and laterally until 

 the whole metathorax is suffused except the zones occupied by the 

 longitudinal stripes. It will thus be seen that the two median yellow 

 stripes commonly present occupy positions between the middle and the 

 two lateral pigmented areas, while the two lateral stripes occupy zones 

 external to the lateral pigmented areas. 



Meanwhile pigment has appeared at the base of the anterior abdom- 

 inal segments (PI. II, fig. 22;. In the first segment the area is quad- 

 rangular and gradually fades out posteriorly. In the second it takes 

 the form of a shallow triangle of varying altitude. In addition, there 

 is a series of dark metameric spots which correspond in position with 

 the spiracular muscles, and in the second segment there is a second 

 transverse band just posterior to the middle zone and coinciding with 

 the zone where pigment first appears in the third segment. 



The pigmented areas have at first a light brownish-drab color. This 

 gradually deepens, the areas where the colors first appeared remaining 

 at first darker than the margins of the pigmented area. The deepening 

 hue here becomes fuscous, and finally in man}^ cases almost entirely 

 black. 



In the segments posterior to the second, the pigmented triangle is 

 shallower and its base extends entirely across the anterior aspect of 

 the segment. In these zones the pigment gradually deepens, and from 

 them it spreads to suffuse the whole integument excepting those zones 

 which are to be yellow in the adult. The latter retain the original 



