1858.] CLIMATE AND MIGRATION. 493 



with new forms would be very liable to be improved or modi- 

 fied by natural selection, to adapt them to the new forms 

 with which they had to compete ; hence most of the forms 

 on the mountains of the Tropics are not identical, but rep" 

 resetitative forms of North temperate plants. 



There are similar classes of facts in marine productions. 

 All this will appear very rash to you, and rash it may be ; 

 but I am sure not so rash as it will at first appear to you : 

 Hooker could not stomach it at all at first, but has become 

 largely a convert. From mammalia and shallow sea, I believe 

 Japan to have been joined to main land of China within no 

 remote period ; and then the migration north and south be- 

 fore, during, and after the Glacial epoch would act on Japan, 

 as on the corresponding latitude of China and the United 

 States. 



I should beyond anything like to know whether you have 

 any Alpine collections from Japan, and what is their charac- 

 ter. This letter is miserably expressed, but perhaps it will 

 suffice to show what I believe have been the later main mi- 

 grations and changes of temperature. . . . 



C. Darwin to J. D. Hooker. 



[Down] Oct. 6th, 1858. 



... If you have or can make leisure, I should very much 

 like to hear news of Mrs. Hooker, yourself, and the children. 

 Where did you go, and what did you do and are doing? 

 There is a comprehensive text. 



You cannot tell how I enjoyed your little visit here. It 

 did me much good. If Harvey is still with you, pray remem- 

 ber me very kindly to him. 



... I am working most steadily at my Abstract, but it 

 grows to an inordinate length ; yet fully to make my view 

 clear (and never giving briefly more than a fact or two, and 

 slurring over difficulties), I cannot make it shorter. It will 

 yet take me three or four months ; so slow do I work, though 

 never idle. You cannot imagine what a service you have 



