248 COLOUR IN NATURE chap. 



partial or complete albinism, although there is some 

 doubt how far the comparison is legitimate. White 

 patches are certainly often a sign of specialisation, 

 and are not infrequently confined to the males. In 

 the male of the king paradise bird {Cicinnurus 

 regius) the ventral surface of the body is a pure 

 white, adding greatly to the beauty of the colora- 

 tion ; but the white feathers are a deep ashy-gray at 

 their bases, and there can be little doubt that this 

 is merely one of those cases of sifting of colour 

 which are so characteristic of many male birds. The 

 physiological meaning of cases like that of the 

 gannet, however, wher& there seems to be a complete 

 disappearance of colour, is very obscure ; to suggest 

 that it is due to a constitutional change does not 

 appear to advance the question much. 



In connection with the subject of albinism it may 

 be well to mention that the converse variation, that 

 of excess of pigment, is said to occur both in the 

 case of melanin and lipochromes, giving rise to 

 melanism or erythrism. The fact that neither of 

 these can be associated with the functional dis- 

 abilities which are usually believed to result from 

 total albinism puts them upon a somewhat different 

 plane, but the whole question is diilScult and doubt- 

 ful. The same may be said of some other facts 

 relating to colour, such as the tendency to melanism 

 said to be exhibited by birds occurring in islands. 



Another question of some interest is whether a 

 change of colour can be effected in the plumage 

 without a previous moult. This is strongly sup- 

 ported by some authorities and as strongly denied 

 by others. Gatke, in his Heligoland as an Ornitho- 



