1 48 Appendix. 



seasonally dimorphic, and both apparently restricted in 

 their winter broods to the form corresponding to B of 

 TJiaros. In their summer generation both these species 

 closely resemble the summer form of Tharos, and it is 

 remarkable that these two species, which are the only 

 ones (with the exception of the doubtful Batesii) closely 

 allied to Tharos, should alone be seasonally dimorphic 

 out of the large number of species in the genus. 



Mr. Edwards thus explains the case under considera- 

 tion : "When Phaon, Vesta, and Tharos were as yet 

 only varieties of one species, the sole coloration was that 

 now common to the three. As they gradually became 

 permanent, or in other words, as these varieties became 

 species, Tharos was giving rise to several sub-varieties, 

 some of them in time to become distinct and well 

 marked, while the other two, Pkaon and Vesta, remained 

 constant. As the climate moderated and the summer 

 became longer, each species came to have a summer 

 generation ; and in these the resemblance of blood- 

 relationship is still manifest. As the winter generations 

 of each species had been much alike, so the summer 

 generations which sprung from them were much alike. 

 And if we consider the metropolis of the species Tharos, 

 or perhaps of its parent species, at the time when it had 

 but one annual generation, to have been somewhere be- 

 tween 37 and 40 on the Atlantic slope, and within 

 which limits all the varieties and sub-varieties of both 

 winter and summer forms of Tharos are now found' in 

 amazing luxuriance, we can see how it is possible, as the 

 glacial cold receded, that only part of the varieties of 

 the winter form might spread to the northward, and but 

 one of them at last reach the sub-boreal regions and 

 hold possession to this day as the sole representative of 

 the species. And at a very early period the primary 

 form, together with Phaon and Vesta, had made its way 

 southward, where all three are found "now." 



