226 CALIFORNIA ACADEMY OF SCIENCES. 



a very important one. In his " Organic Evolution " he 

 discusses the changes caused by food, climate, and the 

 direct action of the color of the environment upon the 

 nervous system. This latter influence, which is so im- 

 portant a factor in the changes of color of the frog, for 

 example, probably does not affect birds to any extent 

 whatever, and need not be discussed here. Compara- 

 tively few experiments have been attempted to deter- 

 mine to what extent food may affect the colors of birds. 

 With regard to the effects of food upon color, Mr. Frank 

 Beddard says:* "If the nature of animal colours is 

 borne in mind, it seems impossible to doubt the modi- 

 fying action of food; those that are due to structural 

 peculiarities of the parts coloured (e. g. feathers of many 

 birds) may be altered just as much as those that are 

 caused by the deposition of pigment; for the 'struc- 

 tural ' colours depend largely upon pigment for their 

 manifestation. 



The mere increase in the deposition of pigment 

 may lead to an alteration of colour, oftenest perhaps in 

 the direction of melanism; and there is evidence that 

 various substances, when taken into the body, do influ- 

 ence the amount of excreted matter. Where there is 

 an obvious relation between waste matter and the skin 

 pigments, it cannot be doubted that variation in the 

 amount only of the food may lead to colour changes." 



These remarks of Mr. Beddard's are along the line of 

 a theory of melanism and albinism, suggested to me 

 by Dr. Stejneger, viz.: That there is a general tendency 

 among birds to assume a uniform coloration — generally 

 black, which is prevented from asserting itself in most 

 instances by natural selection, etc. White, Dr. Stejn- 

 eger regards as a mark of degeneration, and, just as 



* Animal Coloration, p. 48. 



