44 COI.ORATION IN POLISTES. 



extreme melanic condition of P. variatus, and in most cases passes far 

 beyond it. The relation between the two is illustrated in Plate II, 

 figs. 24 to 27. 



The Red-Brown Species. 



The pigmentation of P. generostis, and of a similar though smaller 

 red-brown species, was also studied. Here again there is remarkable 

 resemblance between the steps of the process and that already described 

 for variahcs. The pupa at first is of a uniform cream color, which 

 deepens to flesh color, and later, while the pigmentation is progress- 

 ing, acquires a distinct orange cast (PI. II, fig. 32). The zones of the 

 thorax where the pigment first appears are identical with those of 

 P. variahcs, with this exception, that they are more restricted laterally 

 (PI. II, fig. 30). As the process goes on, the coloration in these zones 

 may remain deepest, and thus give rise to the pattern so usual to the 

 thorax of these forms. 



In the abdomen we find the pigmentation of the anterior segments 

 in advance of the posterior ones. It occurs in the form of an irregular 

 surface on the first segment, a triangle with an acute apex at the 

 anterior end of the second segment, and posterior to this a broad 

 band. Although the pigmented zones of the following segments do 

 not appear until a little later, they nevertheless spread rapidly enough 

 to complete the uniform coloration by the end of the pupal stage. 

 Sometimes, however, the deeper pigmentation of these zones persists in 

 all, but more usually it persists only in the anterior segments, thus giv- 

 ing rise to the red-brown abdomen characteristically varied with black. 



Hence we see that, aside from differences in tinge shown by the vari- 

 ous types, the origin and steps of the process of coloration are essen- 

 tially the same in widely differing species. There is good evidence for 

 that persistence in the adults of different species, of different ontoge- 

 netic states which plays so important a part in the coloration theory of 

 Eimer. But this at best would be but a partial explanation of the 

 phenomenon. I have therefore attempted to see whether I could not, 

 by an histological and chemical examination of the pigment, arrive at 

 any causal relation between the resulting color pattern and the condi- 

 tions under which pigmentation takes place. 



