The Wallace-Darwin Correspondence 



families, genera, and species) in North America during the 

 whole Tertiary epoch is, however, the great feature, which 

 assimilates it to Europe and contrasts it with South 

 America. True camels, hosts of hog-like animals, true 

 rhinoceroses, and hosts of ancestral horses, all bring 

 North America much nearer to the Old World than it is 

 now. Even the horse, represented in all South America 

 by Equus only, was probably a temporary immigrant from 

 the North. 



As to extending too far the principle (yours) of the 

 necessity of comparatively large areas for the development 

 of varied faunas, I may have done so, but I think not. 

 There is, I think, every probability that most islands, etc., 

 where a varied fauna now exists have been once more ex- 

 tensive, e.g. New Zealand, Madagascar. Where there is no 

 such evidence (e.g. Galapagos), the fauna is very restricted. 



Lastly as to want of references; I confess the justice of 

 your criticism. But I am dreadfully unsystematic. It is 

 my first large work involving much of the labour of others. 

 I began with the intention of writing a comparatively short 

 sketch, enlarged it, and added to it, bit by bit; remodelled 

 the tables, the headings, and almost everything else, more 

 than once, and got my materials into such confusion that 

 it is a wonder it has not turned out far more crooked and 

 confused than it is. I, no doubt, ought to have given refer- 

 ences; but in many cases I found the information so small 

 and scattered, and so much had to be combined and con- 

 densed from conflicting authorities, that I hardly knew 

 how to refer to them or where to leave off. Had I referred 

 to all authors consulted for every fact, I should have greatly 

 increased the bulk of the book, while a large portion of the 

 references would be valueless in a few years owing to later 

 and better authorities. My experience of referring to refer- 

 ences has generally been most unsatisfactory. One finds, 



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