8 COLORATION IN POLISTES. 



Thus, to determine whether the color variation was continuous or 

 discontinuous, and in what sense it might be adaptive, a study of 

 individual variation was undertaken, and these variations were in turn 

 related to specific distinctions. In the same manner the study of the 

 ontogenesis of the color pattern was made to test the validity of Eimer's 

 hypothesis, and, further, for the purpose of learning whether the 

 characters were in any sense auto-adaptive, the chemical and physical 

 nature of the pigment was considered in connection with the individual 

 variation and the geographical distribution of the various types of 

 color-marking in Polistes and allied genera. 



Accordingly this investigation falls into the following divisions : 



General account. 



Individual variation in the color pattern of Polistes. 



Ontogenesis of the color pattern. 



Physical and chemical nature of the pigment. 



Geographical distribution of the types of color-marking. 



General laws governing color differentiation. 



General consideration with respect to various theories of evolution. 



Summary andi;onclusion. 



I wish to acknowledge my indebtedness to all those who by ready 

 counsel and unfailing sympathy have made the prosecution of this 

 research a real pleasure to me : To Prof. Charles B. Davenport, 

 University of Chicago, who for two years directed the course of 

 these studies, whose enthusiastic interest has been a constant source 

 of inspiration, while his profound knowledge has kept me aloof from 

 many errors ; to Dr. William M. Wheeler, the American Museum of 

 Natural History, New York, to whose suggestion is due the incep- 

 tion of this work and whose wise counsel has from the beginning been 

 very helpful to me ; to Prof. Charles O. Whitman, University of Chi- 

 cago, for the privilege of studying at the Marine Biological Laboratory 

 at Woods Hole, Mass., and for a courteous interest in the progress of 

 this work ; to Mr. W. H. Ashmead for the loan of the collection of 

 Polistes from the National Museum, Washington, D. C. ; to Mr. 

 Samuel Henshaw for the privilege of examining collections at the 

 Museum of Comparative Zoology, Cambridge, Mass.; to Mr. William 

 J. Fox for courtesies extended tome while studying at the Philadelphia 

 Academy of Natural Sciences ; to the authorities of the John Crerar 

 Library, Chicago, for generously supplying me with rare literature on 

 the subject ; to the following, who, by loans or gifts of material or 

 timely suggestions, have contributed to the successful issue of this 

 work : Mr. C. C. Adams, University of Michigan ; Miss Elizabeth 

 Meek, Bellefonte, Pa. ; Mr. Axel Melander, University of Chicago ; 

 Mr. Charles T. Brues, Columbia University ; Miss Matilda W^ichten- 

 dahl, Gotha, Fla, ; Dr. Harold Heath, Leland Stanford Junior Uni- 



