Introduction. 35 



probably represents the truth— namely, that, among 

 the higher animals, more or less conspicuous pecu- 

 liarities of colour have often been acquired for the 

 purpose of enabling members of the same species 

 quickly and certainly to recognize one another. 

 This theory was first published by Mr. J. E. Todd, 

 in 1888, and therefore but a short time before its 

 re-publication by Mr. Wallace. As his part in the 

 matter has not been sufficiently recognized, I should 

 like to conclude this introductory chapter by drawing 

 prominent attention to the merits of Mr. Todd's 

 paper. For not only has it the merit of priority, but 

 it deals with the whole subject of " recognition 

 colours" — or, as he calls them, "directive colours" — 

 in a more comprehensive manner than has been done 

 by .any of his successors. In particular, he shows 

 that the principle of recognition-marking is not re- 

 stricted to facilitating sexual intercourse, but extends 

 also to several other matters of importance in the 

 economy of animal life ^. 



Having thus briefly sketched the doctrines of the 

 sundry Post-Darwinian Schools from a general point 

 of view, I shall endeavour throughout the rest of this 

 treatise to discuss in appropriate detail the questions 

 which have more specially come to the front in the 

 post-Darwinian period. It can scarcely be said that 

 any one of these questions has arisen altogether de 

 novo during this period ; for glimmerings, more or 

 less conspicuous, of all are to be met with in the 

 writings of Darwin himself. Nevertheless it is no 

 less true that only after his death have they been 



' American Naturalist, xxii. pp. 201-30^. 

 D 2 



