THE WONDER OF LIFE 547 



lampblack, no change follows the transference to a white 

 surface, which shows that the external colour first affects 

 the eyes, then the central nervous system, and then the 

 pigment-cells in the skin. 



It is very instructive to compare the juvenile and the 

 adult coloration. In many young mammals and birds, 

 as Dr. Chalmers Mitchell has well shown in his Childhood 

 of Animals, the coloration requires Uttle more than a 

 physiological interpretation. The pigments are by- 

 products of the metaboHsm ; they are laid down in agree- 

 ment with the particulate character of the sMn, or they 

 may express the rhythms of growth — ^being laid down, for 

 instance, in concentric lines and cross-bars. If this primi- 

 tive coloration is not disadvantageous, it will, of course 

 be tolerated, but the point is, that it does not require any 

 special utilitarian explanation. It may, indeed, be quite 

 useful — ^thus the spottiness of some young mammals 

 makes them very inconspicuous. As the young creature 

 grows its coloration changes. The spots may unite into 

 stripes or bands, or they may be blurred into a monotone. 

 Or it may be that a new pattern replaces the primitive one ; 

 sometimes of ruptive vividness, so that the natural outlines 

 of the animal are broken up protectively; sometimes of 

 startHng and impressive brilliance, such as we see in certain 

 sex-decorations. It is when we pass to the secondary 

 coloration, analysed out of the primary as anihne dyes 

 from the coal-tar residue, that we feel the need of special 

 utilitarian or selectionist interpretations. And they are 

 not lacking ! 



Warning Coloration. — ^A third use of coloration, 

 first expoimded by Alfred Russel Wallace, is as an advertise- 

 ment on the part of animals that are unpalatable or offensive 



