Mutations among Birds 
A well-marked mutation which appears regu- 
larly in nature is the red-headed variety of the 
beautiful Gouldian Finch (Péephila mirabilis ) 
of North Australia. Normally the head of the 
cock is black, but in about ten per cent. of the 
individuals the cock has a crimson head, while 
that of the hen is dull crimson and black. | 
Mutations which occur with such regularity 
are certainly rare. On the other hand, there are 
certain mutations which we may expect to see 
appear in any species of plant or animal. 
Albinistic forms are a case in point, and less 
frequently we see white varieties which are not 
pure albinos, because the eye retains some at 
least of the normal pigment. As examples, we 
may cite white dogs, cats, fowls, horses, ducks, 
geese, and Java sparrows among domesticated 
animals, and the white forms of the Amazonian 
dolphin and of the giant Petrel of the South 
seas (Osstfraga gigantea) among wild creatures. 
In a white mutation the eye may lose all its 
pigment, and then we have a true albino, Such 
forms on account of their imperfect vision cannot 
survive in a state of nature, hence no wild pink- 
eyed species are known. 
Or the eye may display a partial loss of pig- 
ment, as, for example, in the white domestic 
forms of the common goose, the Chinese goose, 
and the Muscovy duck. Finn saw a case in 
which the eyes of a pink-eyed rabbit changed 
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