ii6 COLOUR IN NATURE chap, v 



Krukenberg in considering that it is nutritive in 

 function, apparently regarding it as of importance 

 in the nutrition of the young individuals. This case 

 is of some interest, because it is so common to find 

 coexisting with the so-called excretory pigments 

 others whose function is unknown or doubtful, but 

 which are apparently not excretory. 



It is also of interest to notice that the so-called 

 respiratory pigments, those which are capable of re- 

 peated oxidation and deoxidation, frequently occur 

 in organisms where it is exceedingly doubtful whether 

 they have really respiratory significance. 



