268 Mr. C. F. M. Swynnerton 07i the 



most useful one, and likely to be selected wherever that is 

 possible, for impressing the enemy's memory and facilitating 

 recognition, and for differentiating a nauseous animal the 

 more strongly from those numerous species that have to 

 depend instead on inconspicuousness for safety. 



Distinctive Coloration. — This was explained by Wallace 

 as having come about in response to the necessity for 

 recognition by members of the same species, and " the 

 wonderful diversity of colour and of marking that prevails, 

 especially in birds and insects,'' was ascribed "to the fact 

 that one of the first needs of a new species would be, to 

 keep separate from its nearest allies, and this could be most 

 readily done by some easily seen external mark of difference " 

 ('Darwinism/ 1889, p. 218). 



No one who has studied animals in the field from this 

 point of view, can have failed to observe that Wallace was 

 right, so far as birds were concerned, in attaching the very 

 highest importance to the above factor. I could myself 

 adduce numerous and striking instances of the use of their 

 distinctive colouring and distinctive call-notes and displays 

 by birds of the same species for keeping in touch, for joining 

 up when widely separated and with numerous birds of other 

 species in between, and for recognition generally. 



That yet another factor besides this, and besides sexual 

 selection, may, nevertheless, have contributed to the pro- 

 duction of distinctiveness and diversity in the appearance 

 even of adult birds and have been, perhaps, mainly 

 responsible for it in certain other directions, is rendered 

 likely by the results of my food-preference experiments. 

 Using insects as prey, I found, whatever vertebrate enemy 

 I employed, that not only would it at a given moment 

 emphatically and persistently refuse some insects, while 

 readily eating others, but that the finest gradation occurred 

 between those species (grade Z, let us call them) that it 

 would eat only under stress of hunger, through grades Y, 

 X, W, V, &c., refused ia turn as it gradually " filled up,'' 

 to the very few species (grade A), that it would regularly eat 

 at all stages, right up to repletion point. 



