202 Animal Life and Intelligence. 



adequate explanation of the specific colour-tints of the 

 humming-birds, or the pheasants, or the Papilionidse 

 among butterflies. If, as Mr. Wallace argues, the immense 

 tufts of golden plumage in the bird of paradise owe their 

 origin to the fact that they are attached just above the 

 point where the arteries and nerves for the supply of the 

 pectoral muscles leave the interior of the body, are there 

 no other birds in which similar arteries and nerves are 

 found in a similar position ? Why have these no similar 

 tufts ? And why, in the birds of paradise themselves, does 

 it require four years (for it takes so long for the feathers 

 of the male to come to maturity) ere these nervous and 

 arterial influences take effect upon the plumage ? Finally, 

 one would inquire how the colour is determined and held 

 constant in each species. The difficulty of the Tylor- 

 Wallace view, even as a matter of origin, is especially great 

 in those numerous cases in which the colour is determined 

 by delicate lines, thin plates, or thin films of air or fluid.* 

 Under natural selection, as we have seen, the develop- 

 ment of colour is fostered under certain conditions. The 

 colour is either protective, rendering the organism incon- 

 spicuous amid its normal surroundings, or it is of warning- 

 value, advertising the organism as inedible or dangerous, 

 or, in the form of recognition-marks, it is of service in 

 enabling the members of a species to recognize each other. 

 Now, in the case of both warning colour and recognition- 

 marks, their efficacy depends upon the perceptual powers 

 of animals. Unless there be a rapidly acquired and close 

 association of the quality we call nastiness with the quality 

 we call gaucliness (though, for the animal, there is no such 

 isolation of these qualities as is implied in our words t), 

 such that the sight of the gaudy insect suggests that it 

 will be unpleasant to eat, the gaudiness will be of no avail. 

 And if there is any truth in the doctrine of mimicry, the 

 association is particular. It is not merely that bright 



* Mr. Poulton, who takes a similar line of argument in his " Colours of 

 Animals," lays special stress upon the production of white (see p. 326). 

 t See Chapter VIII. 



