12 COLORATION IN POLISTES. 



POLISTES VARIATUS CRESSON. 



GENERAL TYPE OK VARIATION. 



Some 1,300 specimens of this wasp were collected in the summer of 

 1899, most of them directly from the nest. The collection represents 

 the condition of the species in a region not over 4 miles square at Hart- 

 land, in southeastern Wisconsin. In this and other groups considered, 

 certain conspicuously varying characters will be selected, the modal 

 or prevailing condition and the kind and extent of variation determined, 

 and a study made of the correlation of this character with other varying 

 color characters. I transcribe on page 84 Cresson's description of the 

 species as given in his Texan Hymenoptera. 



Upon inspection the most conspicuously varying character proved to 

 be the metameric spot of the second abdominal segment. A number 

 of conditions were selected as typical for some part of the collection, 

 and the specimens, numbering 1,278, were then grouped about these 

 characteristic conditions, no regard being paid to the colony from which 

 the specimen had been derived. Plate I shows the different types, and 

 of these, figs, i and 2 represent most nearly the condition described 

 by Cresson. Here the segment is ornamented on each side by a large 

 irregular yellow blotch, which is slightly tinged on the edges with 

 ferruginous. The borders are broad and well defined and slightly 

 interrupted medially. In fig. i the ferruginous margin is entirely 

 lacking, the borders being much the same as before, while fig. 2 

 represents the opposite tendency with narrowing borders and the fer- 

 ruginous margins encroaching on the yellow of the metameric spots. 

 In fig. 2 the yellow or ferruginous spots are exceedingly small, and 

 in fig. 3 they are absent altogether, the borders being narrow and 

 less well defined. Figs. 7 and 8 represent conditions where the pattern 

 is similar to those already described, but the prevailing tint is more of 

 a russet than in the other specimens. 



It was soon found that innumerable transitions existed between the 

 various types, so that the collection, instead of falling into well defined 

 groups, formed a continuous whole, which exhibited along several 

 lines a progressive tendency from a less to a more melanic condition. 

 Further, the study of the development of the color pattern in the pupa 

 showed that the dark pigment gradually comes in on a uniform light 

 groundwork, spreads from definite centers, and just before emergence 

 the areas which are still unpigmented are filled in, so to speak, with 

 the hypodermal yellow. The condition of the collection with refer- 

 ence to the various types may, therefore, be described in the following 

 terms, while their relations will be made clear by inspection of fig. 7. 



