274 



THE AMERICAN NATURALIST [Vol. LI 



phism, and polymorpliism all have the same biological 

 significance, i. e., that they represent different ways in 

 which the coloration of a species exercises its obliterative 

 function in a greater variety of circumstances than would 

 l)e possible if it were uniform. Upon this view of the 

 matter there would seem to be no reason why color vari- 

 ations of the seasonal sort should not provide material 

 for evolution by natural selection. 



Before suggesting another possible explanation of the 

 fact of mimetic resemblance it seems desirable to state 

 more specifically why certain of those already mentioned 

 seem improbable. 



Some color patterns are apparently limited to fishes 

 whose habits are similar. Others occur which have sur- 

 vived the introduction of marked structural changes and 

 are now the common property of whole families or groups 

 of families, whose manner of living varies decidedly from 

 species to species. There is one such system of coloring 

 among grunts, groupers and snappers (HaemulidgB, 

 Epiueplielinai, and Lutianidae), and Labrids and Scarids 

 share another. In each pattern modifications may be 

 noted which seem particularly appropriate under the local 

 conditions in which they appear. Individual elements 

 may lose all semblance of the original, and yet the nature 

 of the whole be not obscured. But these facts make one 

 skeptical regarding Thayer's hypothesis, for if, in but- 

 terflies too, detail is less important than the appropriate 

 effect of the whole, the probability is remote that for dif- 

 ferent environments complex, ideal, protective or conceal- 

 ing patterns exist, whose slightest spot is so significant 

 that there is marked tendency for forms of different racial 

 endowment to attain them, if their habits are si 



The same facts militate against such a con' 

 Packard's, that mimicry is a result of similar - 

 the direct influence of one set of external conditions. F 

 coloration is characterized by such conservatism or in- 

 ertia, and the same elements of pattern appear in such a 

 variety of habitats, that the power of environmental ' 



