COLORATION IN POLISTES. 21 



CoRRKLATioNS Between Pattern of Abdomen and Other Cor.oR 



Characters. 



Attention has already been directed to the fact that the three main 

 trends of divergence from the normal condition of the abdomen are in 

 the direction of three different species, viz, P. ca7iadcnsis{V\. IV, fig. 41), 

 P. aurijer (PI. Ill, fig. 33), and P. pallipes (PI. Ill, fig. 34). For the 

 detailed description of these species reference is made to the table of 

 species given at the close of this paper, but in brief we may describe the 

 first of these as characterized by having the usual pattern, more or less 

 obscured by fuscous, tending toward the production of a uniform dull 

 brown coloring ; the second by being predominantly yellow ; the third 

 predominantly black. (See PI. I, figs. 1-8.) 



In the first series of P. variatus the fuscous tendency affects equally 

 all parts of the external anatomy ; but since the members are separated 

 distinctly from cajiadensis in point of size, and as, moreover, it is some- 

 what doubtful whether in some cases this appearance may not be due 

 to the imperfect drying of the wasp after emergence, attention will be 

 concentrated on the last two trends. 



P. aiirifer is described as possessing a yellow clypeus and yellow 

 abdomen, with a black triangle at the base of the first and second seg- 

 ments. The thorax possesses the usual yellow borders, and there are 

 yellow lines on the metathorax. Examination of any series of speci- 

 mens of P. aiuifer shows this condition of the abdomen to be produced 

 by the enlarging of the yellow segmental borders and their confluence 

 with the enlarged lateral spots. The anterior portion of each segment 

 is black, but by telescoping these segments the black of all the seg- 

 ments excepting the first two is entirely hidden, and the abdomen 

 appears to be predominantly golden. The typical aurifer is not de- 

 scribed as having any ferruginous in the abdomen, but any series of 

 specimens so named always shows more or less of that color in the 

 same areas as does P. variatus. The clypeus, too, occasionally shows 

 a trace of pale ferruginous in one or two points near its base. P. 

 aurifer, therefore, may be regarded as a variatus where the black has 

 been left out of the clypeus and correspondingly reduced in the abdo- 

 men — an exaggeration of the xanthic trend of variation. 



On the other hand, a condition similar to that described by I^epeletier 

 for pallipes (see p. 81) might be obtained in either of the melanic 

 trends by the spread of the dark pigment to obscure some or all of the 

 borders and the greater part of the yellow markings of the thorax and 

 abdomen. 



P. variatus merges into P. pallipes as we pass eastward, and into P. 

 aurifer as we cross the plains to the south westward. Therefore, if we 



