THE COLOKATION OF ANIMALS 81 



who can prove that the best and inost familiar protective colouring 

 really protects its possessors'? What if, after all, it is all a game, 

 a joke, which the Creator is playing with us poor mortals ? Did not 

 a trustworthy observer recently watch carefully, and see how a pair 

 of sparrows daily cleared a wooden fence on which moths of the 

 genus Catocala and other species of nocturnal Lepidoptera, excellently 

 furnished with protective colours, were wont to settle by day ? They 

 did their work thoroughly, and hardly overlooked a single individual. 

 But who has a right to see anything more in this than — what surely 

 goes without saying — that the best protective colouring is not an 

 absolute protection, and never preserves all from destruction, but 

 always only some, and it may be very few. 



How else could there be such a high ratio of elimination, and 

 such a constancy in the number of individuals of a species on any 

 unchanging area? These sparrows had simply made full use of 

 an experience, probably acquired by chance to begin with, and their 

 vision had become sharpened for this particular species on the almost 

 similarly coloured wooden fence, just as that of the expert butterfly 

 collector does. It certainly does not follow from this that the 

 protective colouring was useless, nor can we regard the harmony 

 between the protruding tip of the anterior or posterior wing and the 

 large protectively coloured surface of the covering wing as of no 

 importance. On the contrary, if the tips were white or con- 

 spicuously coloured like the rest of the posterior wing, they would 

 assuredly attract the sharp eye of hungry enemies to the spot, and so 

 betray the victim. Instead of this, the spot in question is not only 

 dark, but, in the case of Notodonta, is furnished with a tuft of hairs, 

 which, in the insect's resting position (Fig. 12, B), lies on the back, 

 and looks like a dark, somewhat curved projecting tooth, in front 

 of which there stands another, quite similar, which arises from the 

 anterior wing, and behind there are other seven, rather smaller, 

 dark teeth of the same kind, springing from the outer edge of the 

 anterior wing. Taken altogether, they mimic the dentated edge of 

 a withered leaf, and thus, in spite of their diverse origins, form 

 a unified picture, and one with a considerable protective value. How 

 is it possible to doubt that each of these hair-tufts has arisen under 

 the influence of natural selection, and that its absence or imperfect 

 development might result in the discovery and elimination of the 

 insect concerned 1 



These cases seem to me particularly beautiful proofs of the 

 productive efficiency of selection. The wing is protected just 

 as far as it protrudes from beneath the other — not a millimetre 



