l86l.] MR. BATES. 36l 



of the ' Origin/ and crawling on most slowly with my 

 volume of 'Variation under Domestication.' .... 



[The following letter refers to Mr. Bates's paper, " Contri- 

 butions to an Insect Fauna of the Amazon Valley," in the 

 4 Transactions] of the Entomological Society.' vol. 5, N.S.* 

 Mr. Bates points out that with the return, after the glacial 

 period, of a warmer climate in the equatorial regions, the 

 4t species then living near the equator would retreat north 

 and south to their former homes, leaving some of their con- 

 geners, slowly modified subsequently ... to re-people the zone 

 they had forsaken." In this case the species now living at 

 the equator ought to show clear relationship to the species 

 inhabiting the regions about the 25th parallel, whose distant 

 relatives they would of course be. But this is not the case, 

 and this is the difficulty my father refers to. Mr. Belt has 

 offered an explanation in his ' Naturalist in Nicaragua ' 

 (1874), p. 266. "I believe the answer is that there was much 

 extermination during the glacial period, that many species 

 (and some genera, &c, as, for instance, the American horse), 

 did not survive it ... . but that a refuge was found for 

 many species on lands now below the ocean, that were 

 uncovered by the lowering of the sea, caused by the immense 

 quantity of water that was locked up in frozen masses on the 

 land."] 



C. Darwin to J. D. Hooker. 



Down, 27th [March 1861]. 



MY DEAR HOOKER, I had intended to have sent you 

 Bates's article this very day. I am so glad you like it. I have 

 been extremely much struck with it. How well he argues, 

 and with what crushing force against the glacial doctrine. 

 I cannot wriggle out of it : I am dumbfounded ; yet I do 

 believe that some explanation some day will appear, and I 



* The paper was read Nov. 24, i860. 



