162 ANIMAL LIFE 



is no large class in which the yellow and red pigments 

 are not to be found, though we may have to search 

 in the remotest and most delicate organs before we 

 find them ; they may confer the most brilliant colour, 

 or be hidden and valueless as regards it. 



The meaning of this widespread colouring is not 

 yet fully understood. It may well be an apparatus 

 of extreme antiquity, which has been to some extent 

 supplemented by newer methods. These pigments 

 are occasionally capable of producing starch in the 

 presence of light, but neither so effectively nor so 

 rapidly as the green colouring matter; and it is not 

 unlikely that the green pigment, which is perhaps the 

 most economic machine that life has evolved, was 

 only perfected after the simpler yellow tools had long 

 been tried for the production of food from inorganic 

 sources in air and water. 



In the lower plants the red and yellow colouring 

 matter is related to the accumulation of fat and oils, 

 which are stored in the seeds or spores. Similarly, in 

 the carrot, the huge reserves of fatty materials col- 

 lected in the roots are accompanied by a dense forma- 

 tion of yellow pigment, and in the eggs of animals the 

 same relation between yolk and pigment is clear. 



So constant is this association that these pigments 

 have been called fatty pigments, and stand in some 

 sort of relation to the nourishment of the young, 

 whether plant or animal. But until recently the 

 nature of this relation was entirely unknown. The 

 results of some researches on the pigments of prawns 



