HIS 'ORIGIN OF SPECIES' 251 



It was after Darwin had got rid of his herculean 

 labours over the ' Cirripede book ' that he began to 

 settle down seriously to the great work of his life 

 the investigation of the origin of the species of plants 

 and animals. One of the three volumes of the Bio- 

 graphy is entirely devoted to tracing the growth of 

 his views on this subject, and the preparation and 

 reception of the great work on the Origin of Species. 

 In no part of his task has the editor shown greater 

 tact and skill than in this. From the earliest jottings, 

 which show that the idea had taken hold of Darwin's 

 mind, we are led onwards through successive journals, 

 letters, and published works, marking as we go how 

 steadily the idea was pursued, and how it shaped itself 

 more and more definitely in his mind. It is impossible 

 to condense this story witm'n the limits of a Review 

 article, and the condensation, even if possible, would 

 spoil the story, which must be left as told in the 

 author's own words. Briefly, it may be stated here 

 that he seems to have been first led to ponder over 

 the question of the transmutation of species by facts 

 that had come under his notice during the South 

 American part of the voyage in the Beagle such as 

 the discovery of the fossil remains of huge animals 

 akin to, but yet very distinct from, the living arma- 

 dillos of the same regions ; the manner in which closely 

 allied animals were found to replace one another, as 

 he followed them over the continent ; and the remark- 

 able character of the flora and fauna of the Galapagos 

 archipelago. ' It was evident,' he says, ' that such facts 

 as these, as well as many others, could only be ex- 

 plained on the supposition that species gradually 



