1 46 Appendix. 



taken from Virginia to the Catskills, suffered no retarda- 

 tion of development. (See Exp. 2.) It might have 

 been expected that all the larvae of this last brood taken 

 to the mountains would have become lethargic, but the 

 majority resisted this change of habit. From all these 

 facts it may be concluded " that it takes time to natura- 

 lize a stranger, and that habits and tendencies, even in a 

 butterfly, are not to be changed suddenly." 6 



It has been shown that Tharos is digoneutic in the 

 Catskills and polygoneutic in West Virginia, so that at 

 a great altitude, or in a high latitude, we might expect 

 to find the species monogoneutic and probably restricted 

 to the winter form Marcia. These conditions are ful- 

 filled in the Island of Anticosti, and on the opposite 

 coast of Labrador (about lat. 50), the summer tempera- 

 ture of these districts being about the same. Mr. Ed- 

 wards states, on the authority of Mr. Cooper, who col- 

 lected in the Island, that Tharos is a rare species there, 

 but has a wide distribution. No specimens were seen 

 later than July 29, after which date the weather became 

 cold, and very few butterflies of any sort were to be seen. 

 It seems probable that none of the butterflies of Anti- 

 costi or Labrador produce a second brood. All the 

 specimens examined from these districts were of the 

 winter form. 



In explanation of the present case Dr. Weismann 

 wrote to Mr. Edwards : " Marcia is the old primary 

 form of the species, in the glacial period the only one. 

 Tharos is the secondary form, having arisen in the 

 course of many generations through the gradually work- 

 ing influence of summer heat. In your experiments 

 cold has caused the summer generation to revert to the 

 primary form. The reversion which occurred was com- 

 plete in the females, but not in all the males. This 



6 Compare this with Weismann's remarks, pp. 19 22, and 53. 



