PREFACE IX 



hinted at here. At the same time I camiot hope to 

 build. That is the task of the great band of workers in 

 many departments of Biology, who, undeterred by failure 

 and urged on by the fire, enthusiasm, and generous aspira- 

 tions of youth, return time after time, generation after 

 generation, to the assault of the fortresses of nature, well 

 knowing that their material reward will be small, that 

 defeat means the world's neglect and that success, except 

 the greatest, brings but a pittance of its esteem. To them 

 I inscribe this book in the hope that it may serve if only to 

 a small extent to smooth over the difficulties of part of the 

 road which at first they have to traverse. 



A. SEDGWICK. 



Trinity College, Cambridge, 

 February, 1905. 



