6 INTRODUCTION 



ingrained are these periodic habits that they are retained 

 even when the animal showing them is removed inland and 

 kept in a perfectly still aquarium. Summer and winter, seed- 

 time and harvest play perhaps the greatest role in this rhythm. 

 One has only to think of the breeding habits of most animals 

 or of the annual appearance and disappearance of the foliao-e 

 of deciduous trees to recognise this. 

 Yes; life, if undefinable, is rhythmic. 



