1876.] GEOGRAPHICAL DISTRIBUTION. 407 



that we must determine the areas, chiefly by the nature of the 

 mammals. When I worked many years ago on this subject, 

 I doubted much whether the now called Palsearctic and Ne- 

 arctic regions ought to be separated ; and I determined if I 

 made another region that it should be Madagascar. I have, 

 therefore, been able to appreciate your evidence on these 

 points. What progress Palaeontology has made during the 

 last 20 years ; but if it advances at the same rate in the future, 

 our views on the migration and birth-place of the various 

 groups will, I fear, be greatly altered. I cannot feel quite 

 easy about the Glacial period, and the extinction of large 

 mammals, but I must hope that you are right. I think you 

 will have to modify your belief about the difficulty of dispersal 

 of land molluscs ; I was interrupted when beginning to ex- 

 perimentize on the just hatched young adhering to the feet 

 of ground-roosting birds. I differ on one other point, viz. 

 in the belief that there must have existed a Tertiary Ant- 

 arctic continent, from which various forms radiated to the 

 southern extremities of our present continents. But I could 

 go on scribbling for ever. You have written, as I believe, a 

 grand and memorable work which will last for years as the 

 foundation for all future treatises on Geographical Distribu- 

 tion. My dear Wallace, yours very sincerely, 



Charles Darwin. 



P.S. — You have paid me the highest conceivable com- 

 pliment, by what you say of your work in relation to my 

 chapters on distribution in the ' Origin,' and I heartily thank 

 you for it. 



[The following letters illustrate my father's power of tak- 

 ing a vivid interest in work bearing on Evolution, but uncon- 

 nected with his own special researches at the time. The 

 books referred to in the first letter are Professor Weismann's 

 ' Studien zur Descendenzlehre,' * being part of the series of 



* My father contributed a prefatory note to Mr. Meldola's translation 

 of Prof. Weismann's ' Studein,' 1880-S1. 



