EXCURSIONS OF AN EVOLUTIONIST 



minds of all the men on whose opinions he set 

 the most value. The success of his theory was, 

 indeed, wonderfully rapid and complete. To 

 understand him was to agree with him, and be- 

 fore ten years more had passed by, so many able 

 men had become expounders and illustrators of 

 the theory of natural selection that as he told 

 me it seemed no longer so necessary as it had 

 once seemed for him to write the larger and 

 more elaborate treatise. The learned work on 

 the "Variation of Animals and Plants under 

 Domestication," which appeared in 1868 in two 

 octavo volumes, formed the first instalment of 

 this long-projected treatise. The second part 

 was to have treated of the variation of animals 

 and plants through natural selection ; and a 

 third part would have dealt at length with the 

 phenomena of morphology, of classification, and 

 of distribution in space and time. But these 

 second and third parts were never published. 



I alluded, just now, to the " unforeseen cir- 

 cumstance " which led Mr. Darwin in 1859 to 

 break his long silence, and to write and publish 

 the " Origin of Species." This circumstance 

 served, no less than the extraordinary success 

 of his book, to show how ripe the minds of men 

 had become for entertaining such views as those 

 which Mr. Darwin propounded. In 1858 Mr. 

 Wallace, who was then engaged in studying the 

 natural history of the Malay Archipelago, sent to 

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