PREFACE 



DURING some ten years' work in a small marine 

 laboratory in Brittany it has fallen to me 

 not infrequently to attempt to explain to curious 

 visitors what were my objects in going to and fro 

 upon the shore, in wading among the sea-weeds and 

 in bringing into the laboratory minute, worm-like 

 animals which represented often my sole "catch." 



I discovered that many of the visitors to the 

 laboratory became interested in the work that 

 was going on, and that, though they disclaimed a 

 knowledge of biology, they followed with under- 

 standing and interest the story of the behaviour 

 and life histories of "the worms": indeed, they 

 succeeded generally in putting to me pertinent and 

 unanswerable questions with respect to these " plant- 

 animals." 



The pleasant recollection of hours spent in this 

 way is responsible primarily for my undertaking to 



