COLOURS OF FATTY PIGMENTS 165 



but for the most part employs a newer and more 

 elaborate method. 



But if the plant-like method of elaborating food 

 from air and water has fallen with animals into disuse, 

 the connection between these old yellow and red pig- 

 ments and nutrition is still an intimate one. We have 

 seen that where fat is formed such pigment is fre- 

 quently, in prawns always, present, and we can now see 

 more significance in the alliance of pigment with fat 

 formed out of food on the newer plan of the digestive 

 system, and accumulated in the skin, muscles, liver, 

 and eggs. 



Nothing is more common than for oil to assume a 

 yellow colour, or for the seed-coats of some plants or 

 the tubers of others to become yellow or red. In the 

 majority of such cases the colour is unessential, and 

 neither concerned in the formation nor accumulation 

 of the stores. 



But as a hint of the part which these ochreous and 

 rufous pigments played in these processes ages ago we 

 have a suggestion of the utmost value, of a former 

 utility, of the need for an historical grip on the facts of 

 nature before their significance can be even imperfectly 

 appreciated. 



From such a broad survey of the green, yellow, and 

 red pigments of plant and animal we acquire a stand- 

 point from which we may view the colours of animals 

 in a new light ; not sufficiently high to enable us to 

 see to the boundaries of knowledge nor to determine 

 with equal clearness foreground and background, but 



