IMIOTKITIVE COLORATION. 



ono moment admitted until the pigments themselves have 

 been studied. There is no inherent improbability in the view 

 that this cause of protective coloration is very widely spread : 

 many colouring substances, as has been already mentioned, 

 are extremely resistant to chemical action. Carmine is used 

 in every physiological laboratory as a means of detecting the 

 paths traversed by substances taken into the body by the 

 alimentary canal, or injected into the blood ; the particles of 

 carmine can be readily traced from one tissue to another, 

 because of their chemical stability. It is at least possible that 

 this may be the case with other substances. From this point of 

 view the variability in the tints and patterns of many animals 

 can be more easily understood ; it will depend upon the 

 variability of the pigments in their food, and upon the amount 

 absorbed and transferred to the skin. 



The fixity of the markings of animals has frequently been 

 made use of as an argument in favour of their secondary 

 meaning : but there are also plenty of instances where there 

 is an infinite diversity of markings and tints, which can be 

 more readily explained in the way that has been suggested. 



An interesting suggestion to the same effect is made by 

 Kirby and Spence in their " Introduction to Entomology." On 

 p. 405 (of the 7th edition), in commenting upon the many 

 insects which escape destruction by simulating the lichens 

 upon which they live, it is remarked that " the caterpillar of 

 Bryojjltila alfffe, when it feeds on the yellow Lichen '/iiniper- 

 inus, is always yellow ; but when upon the grey Lie/" >> 

 saxatiliSj its hue becomes grey. This change is probably 

 produced by the colour of its food." 



Another instance which may be very possibly explained in 

 the same way has been recently made known in America.* 



* Science, vol vi. (1885), p. 9. 



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