48 ANIMAL COLOEATION. 



Effects of Food upon Colour. 



Food has certainly an important effect upon the colours of 

 many animals. Semper, in his " Animal Life," although he 

 quotes a number of cases where food seems to have had in- 

 fluence in affecting colours, is indisposed to accept the 

 evidence. 



If the nature of animal colours is borne in mind, it seems 

 impossible to doubt the modifying action of food; those that 

 are due to structural peculiarities of the parts coloured {e.g. 

 feathers of many birds) may be altered just as much as those 

 that are caused by the deposition of pigment ; for the 

 " structural " colours depend largely upon pigment for their 

 manifestation. 



The mere increase in the deposition of pigment may lead to 

 an alteration of colour, oftenest perhaps in the direction of 

 melanism ; and there is evidence that various substances when 

 taken into the body do influence the amount of excreted matter. 

 Where there is an obvious relation between waste matter and 

 the skin pigments, it cannot be doubted,* that variation in the 

 amount only of the food may lead to colour changes. 



The most interesting case of a colour change produced by 

 different food, with which I am acquainted, is that of the 

 larvas of the large Tortoiseshell butterfly when fed upon 

 nettles. The large Tortoiseshell {Vanessa volychloros) nor- 

 mally feeds upon elm, while the small Tortoiseshell ( V. urticm) 

 is addicted to nettles. Mr. J. Tawell submitted to the late 

 Mr. Edward Newman some imagos of the large Tortoiseshell 



* In making some experiments upon the colours of earthworms I 

 confined a large individual in a flower-pot. After the lapse of a month, 

 during which the specimen had been overlooked and the earth allowed to 

 dry up, the worm was found in a cavity in a lump of dry earth, perfectly 

 healthy in appearance", but bleached ; this I attribute to its not having fed 

 for a long period. 



