PREFACE TO THE ENGLISH EDITION. 



WITH the appearance of Charles Darwin's work 

 "On the Origin of Species," in the year 1858, 

 there commenced a new era in biology. Weary 

 of the philosophical speculations which, at the 

 beginning of this century, had at first been started 

 with moderation but had afterwards been pushed 

 to excess, biologists had entirely let drop all 

 general questions and confined themselves to 

 special investigations. The consideration even of 

 general questions had quite fallen into disuse, 

 and the investigation of mere details had led to a 

 state of intellectual shortsightedness, interest 

 being shown only for that which was immediately 

 in view. Immense numbers of detailed facts were 

 thus accumulated, but they could not possibly be 

 mastered; the intellectual bond which should 

 have bound them together was wanting. 



But all this was changed in a short time. At 

 first only single and mostly the younger naturalists 

 fell in with the new theory of development pro- 

 claimed by Darwin, but the conviction soon 

 became general that this was the only scientifi- 



