1913] Johnson: Pigment Formation in Amphibian Larvae 59 



the epidermal pigments of other sorts and colors to come into 

 greater prominence. 



One must distinguish then between differences in coloration 

 which involve actual differences in the color of one or more of 

 the pigments and those which involve differences in the propor- 

 tional amounts of the different pigments. Although the inhibitors 

 here discussed merely reduce the amount of melanin, instances 

 cited show that the tyrosinase reaction may be so affected by 

 certain chemical substances that the color of the resulting pig- 

 ment is different from that of ordinary melanin. The " factors" 

 postulated by Mendelians may operate in this latter fashion, also 

 the chemical substances cited below which are able to change the 

 color of the plumage of birds undoubtedly act in this way. 



C. THE EELATION OF AMOUNT OF NUTRITION TO 

 PIGMENTATION 



Weismann's view that color is profoundly influenced by 

 nutritive conditions is supported by Tornier's experiments in 

 pigment control. My results with similar experiments, however, 

 do not support this view. 



Tornier (1907, 1908), experimenting with Pelobates larvae, 

 divided the tadpoles into lots for differential feeding. He found 

 that tadpoles receiving a minimum amount of food (algae, 

 together with varying amounts of fish) contained little or no 

 pigment and that by feeding increased amounts of fish it was 

 possible to change the epidermal coloring from white through 

 yellow, red, and grey, to black. Comparable effects were pro- 

 duced by removing a portion of the yolk from the egg. This 

 reduced the nutrition of the animals and produced albinism, 

 erythrinism, or blackness depending upon the state of nutrition. 

 He also found that the experiments could be carried in the 

 opposite direction and that through a diminution of feeding, well 

 fed black larvae could be changed back through a series of colors 

 in the order of black, brown, red, grey, white. He sought to show 

 not only that increase in food supply caused a greater develop- 

 ment of pigment in the chromatophores but also that the pigment 



