EVOLUTION OF THE COLORS OF BIRDS. 201 



this kind will not usually receive a stranger into their 

 midst. While they keep together they are generally 

 safe from attack, but a solitary straggler becomes 

 an easy prey to the enemy; it is, therefore, of the 

 highest importance that, in such a case, the wanderer 

 should have every facility for discovering its companions 

 with certainty at any distance within the range of 

 vision. 



Some means of easy recognition must be of vital im- 

 portance to the young and inexperienced of each flock, 

 and it also enables the sexes to recognize their kind and 

 thus avoid the evils of infertile crosses; and I am in- 

 clined to believe that its necessity has had a more wide- 

 spread influence in determining the diversities of ani- 

 mal coloration than any other cause whatever." 



Mr. J.E. Todd, entirely independently of Wallace, pub- 

 lished in 1888 a similar theory of animal colors, calling 

 them directive colors.* He makes the following classi- 

 fication of directive colors: 1. " Marks and tints, pro- 

 moting recognition at a distance, to guide in straggling- 

 flight and to bring stragglers together [A]. 2. Those 

 indicating the attitude of the body and its probable 

 movement [B] in darkness of night, or in dens; [C] in 

 close movement of large numbers, by day as well as by 

 night; [D] in intercourse of the sexes [E] in the care of 

 young." 



In a previous paperf I have proposed a somewhat dif- 

 ferent classification of recognition markings. Neither 

 Wallace nor Todd seem to have drawn a sharp line of 

 distinction between such recognition marks as enable 

 an individual to find those individuals with which it is 

 to his advantage to consort, as for example, such marks 

 as enable stragglers to regain the flock; and those recog- 



* American Naturalist, xxii, pp. 201-207. 

 t Zoe ii, pp. 210-216. 



