40 COLOUR IN NATURE chap. 
colouring-matter in solution. Now during the breed¬ 
ing season, when the salmon is fasting, the fat which 
is so abundant in the muscles is transferred from 
these to the ovaries, and with the fat the pigment 
is also carried, so that the muscles become pale in 
colour. A very similar process has been described 
by Zopf in the case of a fungus (. Pilobolus ). Here 
in the endospores, the gemmae, and the zygospores, 
drops of oil occur intensely coloured with a lipochrome 
pigment. When the gemmae or spores germinate, 
the oil-drops disappear, and with them the pigment 
also disappears. Zopf in consequence describes this 
pigment as a reserve product. It seems, however, 
safer as yet merely to admit that lipochrome pigments 
frequently occur in association with reserves, leaving 
the question as to whether the pigments themselves 
are capable of being employed in metabolism to be 
determined in the future. It is extremely unlikely 
that the lipochromes are always or even usually of 
the nature of reserves, as they occur in a variety of 
structures where such a significance seems impossible. 
They are extremely common pigments both in plants 
and animals, and we shall have to recur to them very 
frequently in the course of the following pages. 
5. Introduced Pigments 
The last group of pigments that we shall consider 
here includes those which are not produced by the 
organism in which they occur, but are obtained from 
other organisms used as food and are transferred 
apparently almost unaltered to the tissues. The 
colouring-matter of green oysters, which was formerly 
