COLOEATION AFFECTED BY THE ENVIEOXMENT. 55 



made by Dr. Sauermami were particularly interesting. The 

 interest lies in the fact that the pigment was not absorbed 

 equally by all the feathers ; only special tracts were affected; 

 the breast feathers, for instance, became red, while the head 

 remained white. It is therefore quite credible that in a state 

 of nature partial alteration of colour may be produced by a 

 change of diet. 



In the chapter relating to protective resemblances will be 

 found an account of several examples of animals which have 

 apparently acquired a resemblance to their surroundings by the 

 transference of pigment to their bodies in their food. 



Effects of Temperature and Moisture. 



A common colour phenomenon in animals is that known as 

 melanism : by melanism I understand not necessarily a pre- 

 dominance of black, but a general darkening of the coloration. 

 Dr. Scudder, in his magnificent work upon New England 

 butterflies, remarks that melanism is confined to the districts 

 south of New York ; while the reverse condition (viz. albi- 

 nism) is hardly ever found, except north of that city ; this 

 is obviously suggestive of a climatal cause for the colour 

 modifications in question. " As we go north," says Dr. 

 Scudder, " the colours become less sharply defined, then 

 gradually fade away or become blended with surrounding tints; 

 the red first disappears, the blue follows, the yellow longest 

 maintaining its hold." 



Furthermore, according to the same writer, loss of purity of 

 colour and suffusion of markings characterise northern and 



■ Alpine forms of butterflies. Varieties of similar species are 

 commonly met with which exhibit the same suffusion ; these 



' varieties almost exclusively occur in temperate regions, and 

 they have also been artificially produced by cold. 



