X PREFACE 



in a small compass some of the more important facts 

 and considerations that may be found in this great 

 mass of literature, and to present them in such a 

 form that they may be of interest to those who do 

 not possess a specialist's knowledge of genera and 

 species. 



When it was found that animals can and do live 

 even at the greatest depths of the ocean, the interest 

 of naturalists was concentrated on the solution of 

 the following problems. Firstly, do the animals con- 

 stituting the fauna of the abyss exhibit any striking 

 and constant modification in correlation with the 

 physical conditions of their strange habitat ? And, 

 secondly, from what source was the fauna of the 

 abyss derived? Was it derived from the shallow 

 shore waters, or from the surface of the sea ? Is it 

 of very ancient origin, or the result of, comparatively 

 speaking, recent immigrations ? 



These questions cannot be answered in a few lines. 

 Any views that may be put forward regarding them 

 require the support oi % a vast array of facts and 

 figures ; but as the limits of this little book would 

 not permit of my giving these, I have endeavoured 



