164 ANIMAL LIFE 



demands of the body for nourishment and of the eggs 

 for yolk, which cannot be completely met by the usual 

 food, are satisfied. 



The colour of the prawn may thus have nutritive 

 value, though naturally of a lower order than that 

 of the food taken in by the mouth and elaborated 

 in the passage through the tissues. 



The multitudinous minute collections of pigment 

 or chromatophores that star the skin and the interior 

 of the body form so many rudimentary elaborating 

 machines, independent of the digestive system, and 

 differing from it in being able to construct and distri- 

 bute a fatty substance under the influence of coloured 

 light. 



Whether this double mode of nourishment is 

 widely spread amongst animals is not as yet ascer- 

 tained ; but we know that it is extremely difficult to 

 prove, and for this reason skin-nutrition is a mere 

 vestige of an old process that has been supplanted by 

 the more modern and efficient one of nutrition by the 

 digestive system. The collections of pigment, under 

 whose aegis it operates, are somewhat like the buttons 

 on our coat-sleeves, the silent letters in words, or the 

 muscles of our ears relics of a time when ruffles were 

 worn, when those silent historians were vocable, and 

 ears, hairy and pointed, twitched. 



Nature throws nothing away, and in many a secret 

 drawer preserves documents, yellow with age, that 

 hold her past history. Here and there she still uses 

 the old parchment, an ancient recipe to guide the cook, 



