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 cpurse 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 



