CHAPTER III 



THE RELATIONS OF THE ABYSMAL ZONE AND THE 

 ORIGIN OF ITS FAUNA 



In the study of the geographical distribution of 

 terrestrial animals one of the great difficulties met 

 with is the ^impossibility of defining exactly the 

 limits of the regions into which we divide the surface 

 of the earth. In a general way we recognise that 

 there is an Australian region, an Ethiopian region, 

 &c. ; but, when we come to discuss the exact posi- 

 tion of the frontier lines that separate these regions 

 from their neighbours, we find all kinds of difficulties 

 to overcome and inconsistencies to meet. 



For the sake of convenience it is useful to adopt 

 certain arbitrary limits for these regions, notwith- 

 standing these difficulties and inconsistencies, but we 

 must recognise the fact that nature recognises no 

 such limits, that every region overlaps its neighbours 

 to a greater or less extent, and that there are many 



