A Substitute for the Theory of Warning Coloration. 317 



What has happened with coral-reef fish may well have happened with 

 insects. With them also, with few exceptions, the nature of the food pre- 

 cludes selection in the direction of aggressive resemblance. The develop- 

 ment of unpalatability bars in large measure the attacks of vertebrate foes 

 and holds in check selection in the direction of protective resemblance. As 

 a result unpalatable insects have, probably with few exceptions, been free 

 to develop color characters, each according to its kind. This development 

 has. in most cases, resulted in conspicuousness, and to this conspicuousness 

 the term " warning coloration " has been applied. 



For the term warning coloration it would, it seems to me, be better 

 to substitute the term inununity coloration. If the foregoing account is 

 well founded the so-called warning coloration of insects has not been 

 developed by selection, as hitherto believed, and it is not necessary to insure 

 discrimination by insectivorous vertebrates. The term, moreover, covers 

 only certain classes of conspicuousness. while the term " immunity colora- 

 tion " covers all cases of conspicuousness not attributable to selection. Im- 

 munity coloration includes on the one hand the conspicuous color characters 

 of coral-reef fish where it has as its conditioning feature inaccessibility ; 

 it includes also the conspicuous color-characters of those insects which are, 

 for one reason or another, unsuitable as food for vertebrate foes, and here 

 it has as its conditioning feature unpalatability (whether due to stings, 

 pricking hairs, disagreeable juices from the body cavity or glands, hard outer 

 covering, etc.). It probably includes cases of so-called warning coloration 

 among in\ertebrates other than insects {e. g., Coelenterata, nettling nudi- 

 branchs ; see Hargitt, 1904) as well as among vertebrates. That immunity 

 coloration may exist without the screen of unpalatability is shown by the 

 following instances : 



(a) According to Poulton (1887) : 



Wallace has shown that the shape and colors due to sexual selection run riot in 

 localities (certain islands) where enemies are largely excluded by barriers, and in the 

 same way the brilliant colors of nauseous or dangerous insects may perhaps be ex- 

 plained by equal immunity, although due to other causes. 



The work of Mayer (1900) throws serious doubt on the inference that 

 colors such as those that have here run riot are sexual colors in the sense 

 that they have a sexual function, and the whole condition is probably the 

 result of immunit}-. According to Packard (1904) butterflies are not com- 

 monly eaten by birds. Their conspicuousness may therefore be wholly due 

 to immunity. 



ib) Mar-shall and Poulton (1902) make the following statement and 



illustrate it by instances : 



Swift-flying butterflies are not likely to be caught by birds. The latter learn the 

 futility of pursuit. The butterflies have therefore been able to acquire brilliant colors 

 above, particularly those species having protectively-colored undersides. 



