X] MIMICRY AND VARIATION 131 



which the later larval and early pupal stages are passed. 

 By cooling appropriately at the right stage levana can 

 be made to produce levana instead of the prorsa which 

 it normally produces under summer conditions. So 

 also by appropriate warming prorsa will give rise to 

 prorsa. Moreover, if the conditions are properly ad- 

 justed an intermediate form porima can be produced, 

 a form which occurs occasionally under natural con- 

 ditions. The pattern is, in short, a function of the 

 temperature to which certain earHer sensitive stages 

 in this species are submitted. What is true of A. levana 

 is true also of a number of other species. In some 

 cases temperature is the factor that induces the vari- 

 ation. In other countries where the year is marked 

 by wet and dry seasons instead of warm and cold ones 

 moisture is the agent that brings about the change. 

 In some of the South African butterflies of the genus 

 Precis the seasonal change may be even more con- 

 spicuous than in A. levana. In Precis octavia, for 

 example, the ground colour of the wet season form is 

 predominantly red, while in the dry season form of 

 the same species the pattern is different, blue being 

 the predominating colour (cf. PI. VI, figs. 11 and 12). 

 Such examples as these are sufficient to shew how 

 sensitive many butterflies are to changes in the con- 

 ditions of later larval and earlier pupal life. The 

 variations brought about in this way are as a rule 

 smaller than in the examples chosen, but in no case 

 are they known to be inherited, and in no case conse- 

 quently could variation of this nature play any part in 



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