440 GEOGRAPHICAL DISTRIBUTION [CHAP. VI 



Letter 335 travel, and the extremes of modifying cause not so great as 

 the arctics undergo, the result should be considerably modified 

 thereby. Thus : the sub-arctics have (i) to travel twice as 

 far, (2) taking twice the time, (3) undergoing many more 

 disturbing influences. 



All this you have to meet by giving the North temperate 

 forms simply more time. I think this will hardly hold 

 water. 



Letter 336 To J. D. Hooker. 



Down, Nov. 1 8th [1856]. 



Many thanks for your note received this morning ; and 

 now for another " wriggle." According to my notions, the 

 sub-arctic species would advance in a body, advancing so as 

 to keep climate nearly the same ; and as long as they did this 

 I do not believe there would be any tendency to change, but 

 only when the few got amongst foreign associates. When 

 the tropical species retreated as far as they could to the 

 equator they would halt, and then the confusion would spread 

 back in the line of march from the far north, and the strongest 

 would struggle forward, etc., etc. (But I am getting quite 

 poetical in my wriggles). In short, I think the warm-temperates 

 would be exposed very much longer to those causes which I 

 believe are alone efficient in producing change than the 

 sub-arctic ; but I must think more over this, and have a good 

 wriggle. I cannot quite agree with your proposition that 

 because the sub-arctic have to travel twice as far they would 

 be more liable to change. Look at the two journeys which 

 the arctics have had from N. to S. and S. to N., with no 

 change, as may be inferred, if my doctrine is correct, from 

 similarity of arctic species in America and Europe and in 

 the Alps. But I will not weary you ; but I really and truly 

 think your last objection is not so strong as it looks at first. 

 You never make an objection without doing me much good. 

 Hurrah! a seed has just germinated after 21 \ hours in owl's 

 stomach. This, according to ornithologists' calculation, would 

 carry it God knows how many miles ; but I think an owl 

 really might go in storm in this time 400 or 500 miles. Adios. 



Owls and hawks have often been seen in mid- Atlantic. 



An interesting letter, dated Nov. 23rd, 1856, occurs in the Life and 

 Letters, II., p. 86, which forms part of this discussion. On p. 87 the 



