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, where 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 difficult 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- 
