PREFACE. y 



most varied kind, that wide and accurate physio- 

 logical knowledge, that acuteness in devising and 

 skill in carrying out experiments, and that admirable 

 style of composition, at once clear, persuasive and 

 judicial, qualities, which in their harmonious combi- 

 nation mark out Mr. Darwin as the man, perhaps of 

 all men now living, best fitted for the great work he 

 has undertaken and accomplished. 



My own more limited powers have, it is true, enabled 

 me now and then to seize on some conspicuous group 

 of unappropriated facts, and to search out some gene- 

 ralization which might bring them under the reign 

 of known law ; but they are not suited to that more 

 scientific and more laborious process of elaborate in- 

 duction, which in Mr. Darwin's hands has led to such 

 brilliant results. 



Another reason which has led me to publish this 

 volume at the present time is, that there are some im- 

 portant points on which I differ from Mr. Darwin, and 

 I wish to put my opinions on record in an easily 

 accessible form, before the publication of his new 

 work, (already announced,) in which I believe most 

 of these disputed questions will be fully discussed. 



I will now give the date and mode of publication of 

 each of the essays in this volume, as well as the amount 

 of alteration they have undergone. 



I. ON THE LAW WHICH HAS REGULATED THE INTRO- 

 DUCTION OF NEW SPECIES. 



First published in the " Annals and Magazine of 



