70 COLORATION IN POLISTKS. 



GENERAL LAWS GOVERNING COLOR DIFFERENTIATION. 



We have seen that in all Polistes the pattern is produced by the con- 

 currence of two colors : (a) the hypodermal color which occurs in the 

 areas unoccupied by the darker pigment of the chitin, {b) the pigment 

 of the chitinous cuticula. The former is always yellow, varying only 

 slightly for the different species. The latter varies greatly from a 

 shade only slightly darker than the hypodermal yellow to a shade and 

 concentration which approaches black in its effect. The final effect of 

 black is produced by a concentration of at least two kinds of cuticular 

 pigment : {a) dull brown in color, {b) red-brown in color. These two 

 kinds of pigment by their varying amount produce infinite gradation 

 of hue in the genus, and there is good evidence that they are related 

 to each other and to the hypodermal yellow by slight differences in 

 chemical composition. 



With reference to the distribution of these colors in the integument 

 of Polistes the following laws have been formulated : 



(i) The arrangement of the yellow areas is perfectly definite for all 

 representatives of the genus, the yellow when present always occur- 

 ring in the borders or in the form of metameric spots. They are thus 

 related primarily to the external organization of the body, and this 

 relation is most forcibly expressed in the abdomen of the wasp. 



(2) The dark areas are related to the internal structure of the body, 

 for the regions where the color of the chitin occurs most constantly 

 in the different species and earliest in the ontogeny overlie the attach- 

 ment of the principal muscles of the body. 



(3) As far as individual variations occur among the progeny of the 

 same parents, they are continuous, the more aberrant forms proceeding 

 by insensible stages in definite directions from the parent type of mark- 

 ing as a modal condition. 



(4) The cause of the variation among the individuals springing 

 from the same stock is to be sought in slight differences in environ- 

 mental condition. 



(5) The same law holds true for the representatives of a species for 

 a given locality. Here again the variations are continuous and fall 

 into various trends, determined by the predominance of certain envi- 

 ronmental conditions. These trends are impressed as it were upon 

 certain types which are held more or less distinct by inbreeding in the 

 nests — i. e. , tendency toward segregation in very limited areas. 



(6) For the larger areas of distribution the pattern and coloring are 

 again the result of the impress of climatic conditions on the particular 

 type or types which have come to occupy the area. 



