COLORATION IN POLISTES. 77 



crossing, but are preserved and even accumulated by the persistent 

 operation of the external causes. Finally, where the differences between 

 two species occupying the same territory are mainly those of size, as is 

 the case with the carolinus and mbiginosus types of coloration, this may 

 be regarded as illustrating another phase of the principle of segregation, 

 that widely known as the principle of physiological isolation. We 

 conclude, therefore, that specific differentiation in Polistes is in the main 

 due to the influence of external conditions, and within the modes thus 

 established slight variations are due to slight differences in environal 

 conditions ; but these variations tend to cluster about more or less dis- 

 tinct types, which are held thus distinct by the various kinds of isolation 

 resulting from the habits of the insect. 



SUMMARY AND CONCLUSION. 



(1) The colors of Polistes fall into two classes hypodermal and 

 cuticular. 



(2) The hypodermal coloring matter is yellow and is deposited in 

 and among the cells of the hypodermis. 



(3) The cuticular color ranges from a shade scarcely darker than 

 the hypodermal yellow, through varying tones of brown to a shade 

 approaching black. It is due to a brownish pigment which is suffused 

 through the chitinous integument. 



(4) In pattern two main types may be recognized : (a) The multi- 

 colorous, where the cuticular pigment occupies only limited areas and in 

 varying quantity, leaving a more or less conspicuous yellow or yellowish 

 ferruginous ornamentation ; () the unicolorous, where the cuticular 

 pigment extends beyond these areas, so that the whole surface is more 

 or less suffused with the darker color. Numerous transitions exist 

 between these types. 



(5) In the developing color pattern color first appears in certain 

 areas of the uniformly flesh-colored groundwork, and later spreads 

 laterally from these areas as centers until the pattern for the adult is 

 attained. The yellow hypodermal color is the last to appear ; it is laid 

 down in the areas which have been left free from the darker cuticular 

 pigment. 



(6) The areas where the cuticular pigment first appears are con- 

 stant for widely differing species. They represent the points of attach- 

 ment to the cuticula of the more important muscles. 



(7) The various cuticular pigments are related to one another and to 

 the hypodermal yellow by slight differences in chemical composition. 



