ALBINISM. 35 



White, as a normal colour of any species of animal, is comparatively rare in 

 nature. Compared with the immense number of species which inhabit the land- 

 surface of the warm and temperate parts of the globe, which is continuously 

 clothed with dark or richly coloured herbage, rocks, or soil, the number of those 

 of which white is the prevailing colour is infinitely small. On the other hand, 

 birds which habitually dwell among the foaming waves of the sea are usually 

 either partially or entirely white, and white is rather the rule than the exception 

 among the comparatively few inhabitants of the northern regions, where the 

 ground is either permanently or during a considerable portion of the year covered 

 with snow. Under such conditions, white, instead of being the most conspicuous 

 style of colouration, is quite the reverse. The whiteness of these animals must 

 not be confounded with albinism (whiteness occurring accidentally in individuals 

 normally of a different colour). 



ALBINISM. 



Albinism is a condition in which the pigment or colouring matter, usually 

 present in the tissues constituting the external coverings of the body, and which 

 .gives them their characteristic hue, is absent. 



When it occurs, the hair, feathers, etc., are of an opaque white, the claws and 

 bill of a pale horn, and the skin and eyes are pink colour, in consequence of the 

 colour of the blood which circulates through them being no longer concealed by 

 the stronger hues of the pigments. An individual in this condition is called an 

 Albino. 



In complete albinism there is a total abstinence of pigment throughout the 

 :system. This condition occurs occasionally as an individual peculiarity among 

 wild animals, but it has never become perpetuated among them in distinct races 

 or species. 



Partial albinism, a condition in which the absence of pigment is limited to 

 portions of the surface, is much more common as an individual variation, and it 

 ■certainly becomes perpetuated more frequently among domestic than among wild 

 animals. 



MELANISM. 



Melanism is the opposite condition to albinism, and depends on an excess of 

 •dark-coloured pigment in the skin and its appendages — hair, feathers, etc. — beyond 

 what is normally met with in the species. As with albinism, melanism may be 

 partial or complete. When partial, it may occur in either of two forms. In one 

 the black colour may be confined to distinct patches, the remainder of the surface 

 retaining its normal colour ; in the other there is a general darkening of the 

 whole surface not amounting to black. This condition, when transmitted by 

 inheritance and maintained and intensified by natural selection or some similar 

 agency, gives rise to the permanent dark or melanic varieties which occur in 

 many species of animals of various classes in a wild state. Melanism as an 

 individual peculiarity is not so frequent as albinism. It may be congenital or 

 acquired. With birds in confinement this change frequently occurs, and is 

 commonly attributed to errors in diet, especially feeding too freely on hempseed 

 .(Fat. Hist. Museum). 



