476 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1918. 



ness for survival, that adaptation to environment, which should char- 

 acterize animals, if their evolution has proceeded as they suppose. 



Almost by common consent such animals as the hare, woodcock, 

 tree frog, flounder, and a host of others, both terrestrial and marine, 

 are considered obliteratively colored. Indeed, the extent to which 

 the colors, and even the patterns of some of these animals, repeat 

 those of their surroundings, and the difficulty with which they are 

 discovered when at rest, leave little room for dispute regarding the 

 significance of their coloration. But it is otherwise with animals 

 which display patterns of massed colors in sharp contrast with one 

 another and with no obvious tendency to repeat those of the environ- 

 ment in which their possessor may be observed, at least at times. 



Even the general reader who only occasionally seeks diversion in 

 biological literature will recognize in these patterns a familiar bone 

 of contention. To some persons they have seemed to owe their 

 brilliance and conspicuousness to sexual selection. In the opinion of 

 others they warn potential enemies of unpalatability upon the part 

 of their prospective pre} T , and so preserve the latter from unwelcome 

 and dangerous attack. Still others see in such patterns marks devel- 

 oped through ministering to recognition at a distance between mem- 

 bers of the same species. It has also been held that such types of 

 coloration contribute nothing to their possessors' welfare and are to be 

 regarded merely as an indication of their immunity from attack on 

 account of their agility or other advantage they enjoy. Finally, 

 and, as it seemed, most preposterously, until recent events placed the 

 matter in a new light, it has been suggested that they are as truly 

 obliterative in function as others. These patterns of the second sort 

 differ, however, from those of the first in having to discharge their 

 function under different conditions, to which fact they owe their 

 peculiarities. 



For the last suggestion zoology is indebted to Mr. Abbott H. 

 Thayer, 1 whose contribution to an understanding of animal colora- 

 tion has been most substantial. America, however, has been rather 

 backward in expressing appreciation of Mr. Thayer's discoveries. 

 It may therefore be of interest to present in brief certain findings of 

 an entirely independent order wmich consistently support the general 

 principles he enunciates, whose truth and significance are not yet 

 thoroughly comprehended. 



The findings in question 2 are almost exclusively derived from 

 field studies of fishes and Crustacea, which involved the use of equip- 

 ment not commonly employed in such work. The whole may be seen 

 in action in plate 1, figure 1, which shows the launch Darwin, of the 



1 See Abbott H. Thayer, Concealing Coloration in the Animal Kingdom. Macmillan, 

 New York, 1900. 



2 For a detailed statement, see the Journal of Experimental Zoology, vol. 23, 1917, and 

 recent issues of the Year Book of the Carnegie Institution of Washington. 



