Characters as Adaptive and Specific. 217 



II. Food. 



Although, as yet, little is definitely known on the 

 subject, there can be no doubt that in the case of 

 many animals differences of food induce differences 

 of colour within the lifetime of individuals, and 

 therefore independently of natural selection. 



Thus, sundry definite varieties of the butterfly 

 Euprepia caja can be reared according to the different 

 nourishment which is supplied to the caterpillar; and 

 other butterflies are also known on whose colouring 

 and markings the food of the caterpillar has great 

 influenced 



Again, I may mention the remarkable case com- 

 municated to Darwin by Moritz Wagner, of a species 

 of Saturnia, some pupae of which were transported 

 from Texas to Switzerland in 1870. The moths 

 which emerged in the following year were like the 

 normal type in Texas. Their young were supplied 

 with leaves of Jitglans regia, instead of their natural 

 food, J. nigra ; and the moths into which these 

 caterpillars changed were so different from their 

 parents, both in form and colour, "that they were 

 reckoned by entomologists as a distinct species^." 



With regard to moUusks, M. Costa tells us that 

 English oysters, when turned down in the Mediter- 

 ranean, "rapidly became like the true Mediterranean 



' See especially, Koch, Die Raupen und Schmetlerling der Wet- 

 terau, and Die Schmetlerling des Siidwesllichen Deutschlands , whose very 

 remarkable results of numerous and varied experiments are epitomized 

 by Eimer, Organic Evolulion, Eng. Trans, pp. 147-153 ; also Poulton, 

 Trans. Entom. Soc. 1893. 



^ Mivart, On Truth, p. 378. 



