The Origin oj the Markings of Caterpillars. 301 



Spkingidce does not therefore depend upon a con- 

 temporaneous double adaptation, but upon the 

 replacement of an old protective colour by a new 

 and better one, and therefore upon a successive 

 double adaptation. The adult caterpillars of C. 

 Elpenor are not sometimes brown and sometimes 

 green because some individuals have become 

 adapted to leaves and others to the soil, but because 

 the anciently inherited green has not yet been 

 completely replaced by the newly acquired brown 

 coloration, some individuals still retaining the old 

 green colour. 



When, in another place, 9 I formerly stated 

 " that a species can become adapted in this or that 

 manner to given conditions of life, and that by no 

 means can only one best adapted form be allowed 

 for each species," this statement is theoretically 

 correct speaking generally, but not in its applica- 

 tion to the present class of cases. A comparison 

 with one another of those caterpillars which repose 

 by day, distinctly shows that they all possess a 

 tendency to abandon the green and assume a dull 

 colour, but that this process of replacement has 

 advanced further in some species than in others. 

 It will not be without interest to follow this 

 operation in some detailed cases, since we may 

 thus obtain an insight into the processes by which 

 polymorphism has arisen, as well as into the con- 



' " Uber den Einfluss der Isolirung auf die Artbildung." 

 Leipzig, 1872, p. 21. 



