PREFACE 



THIS volume is the outcome of a course of five lectures on 

 " Regeneration and Experimental Embryology," given in Columbia 

 University in January, 1900. The subjects dealt with in the lectures 

 are here more fully treated and are supplemented by the discussion 

 of a number of related topics. During the last few years the prob- 

 lems connected with the regeneration of organisms have interested 

 a large number of biologists, and much new work has been done in 

 this field ; especially in connection with the regenerative phenomena 

 of the egg and early embryo. The development of isolated cells or 

 blastomeres has, for instance, aroused widespread interest. It has 

 become clearer, as new discoveries have been made, that the latter 

 phenomena are only special cases of the general phenomena of 

 regeneration in organisms, so that the results have been treated 

 from this point of view in the present volume. 



If it should appear that at times I have gone out of my way to 

 attack the hypothesis of preformed nuclear germs, and also the 

 theory of natural selection as applied to regeneration, I trust that 

 the importance of the questions involved may be an excuse for the 

 criticism. 



If I may be pardoned a further word of personal import, I should 

 like to add that it has seemed to me that far more essential than each 

 special question with which the biologist has to deal is his attitude 

 toward the general subject of biology as a science. Never before in 

 the history of biology has this been more important than at the 

 present time, when we so often fail to realize which problems are 

 really scientific and which methods are legitimate for the solution 

 of these problems. The custom of indulging in exaggerated and 



