252 
COLOUR IN NATURE 
CHAP. 
describes a considerable number, differing from one 
another by their spectra, their solubilities, or their 
reaction to light. It does not appear that any good 
purpose would be served by giving a list of these 
pigments, at least in our present state of ignorance 
as to the relations of the lipochromes. It is sufficient 
to note that yellow lipochromes occur very frequently 
in the skin, the fat, the yolks of the eggs, and the 
feathers of birds; that these yellow lipochromes 
not infrequently occur mingled with zoonerythrin, 
that yellow feathers may contain two different 
yellow pigments, and that these yellow pigments 
may also be present in feathers which contain too 
much dark pigment for the yellow colour to be 
visible. The appearance of the feather is thus no 
certain criterion of the presence or absence of lipo- 
chrome pigment. 
An exceedingly curious instance of this is afforded 
by Krukenberg’s researches on the colouring-matters 
of Eclectus polychlorus. In this interesting parrot the 
male is chiefly green, with patches of red and blue ; 
the female is chiefly red, with patches of yellow and 
blue ; while, according to Meyer, the young of both 
sexes are red. The blue and green feathers are 
grayish-black on their lower surfaces and appear 
dull-coloured by transmitted light; the yellow and 
red do not change colour by transmitted light. The 
pigments present are one or more dark-coloured 
melanins, a yellow lipochrome, zoofulvin, and red 
“ araroth ” ; the colour differences are in part due to 
structure, in part to the varying amounts of the pig¬ 
ments in the two sexes. This is shown in the 
following- table :— 
