vi PREFACE 



its position among the sciences was followed 

 out in certain directions. The lectures now 

 published represent an attempt at a more 

 comprehensive treatment of the subject. 



The time is now more than ripe for bring 

 ing the great biological movement of the 

 nineteenth century into definite relation with 

 the main stream of human thought; and 

 these lectures form a contribution towards 

 the fulfilment of this task. 



