Appendix, 1 4 7 



proves, as it appears to me, that the males are changed 

 or affected more strongly by the heat of summer than 

 the females. The secondary form has a stronger con- 

 stitution in the males than in the females. As I read 

 your letter, it at once occurred to me whether in the 

 spring there would not appear some males which were 

 not pure Marcia, but were of the summer form, or nearly 

 resembling it ; and when I reached the conclusion of 

 the letter I found that you especially mentioned that 

 this was so ! And I was reminded that the same thing 

 is observable in A. Levana, though in a less striking de- 

 gree. If we treated the summer brood of Levana with 

 ice, many more females than males would revert to the 

 winter form. This sex is more conservative than the 

 male slower to change." 



The extreme variability of P. Tharos was alluded to 

 more than a century ago by Drury, who stated : " In 

 short, Nature forms such a variety of this species that it 

 is difficult to set bounds, or to know all that belongs to 

 it." Of the different named varieties, according to Mr. 

 Edwards, " A appears to be an offset of B, in the direc- 

 tion most remote from the summer form, just as in 

 Papilio Ajax, the var. Walshii is on the further side of 

 Telamonides, remote from the summer form Marcellus" 

 Var. C leads from B through D directly to the summer 

 form, whilst A is more unlike this last variety than are 

 several distinct species of the genus, and would not be 

 suspected to possess any close relationship were it not 

 for the intermediate forms. The var. B is regarded as 

 nearest to the primitive type for the following reasons : 

 In the first place it is the commonest form, predomi- 

 nating over all the other varieties in W. Virginia, and 

 moreover appears constantly in the butterflies from 

 pupae submitted to refrigeration. Its distinctive pecu- 

 liarity of colour occurs in the allied species P. Phaon 

 (Gulf States) and P. Vesta (Texas), both of which are 



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