THE RELATIONS OF THE ABYSMAL ZONE 51 



one that it is most difficult to investigate, and one 

 about which we know but little 



In the present state of our knowledge we cannot 

 divide it into any well-marked sub-zones nor even into 

 geographical regions or sub-regions. It is not divided 

 into sections by any important geographical barriers, 

 and the general characters presented by its fauna are 

 practically the same all the world over. 



Professor A. Agassiz has pointed out in his 

 ' Challenger ' monograph that the deep-sea echinoids 

 of the Atlantic Ocean differ from those living in 

 corresponding depths in the Pacific Ocean, bat it is 

 doubtful whether any such well-marked differences 

 can be observed in other groups of animals. If, in 

 the course of time, increased knowledge of deep-sea 

 animals emphasises the difference between the 

 abysmal fauna of the Pacific and that of the Atlantic, 

 then we can divide this zone into two geographical 

 regions; but at present it seems more correct to 

 consider the abysmal zone as one that is indivisible 

 either bathymetrically or geographically. 



Before passing on to the consideration of the 

 general characters of the abysmal fauna, there are 

 still one or two points that must be just briefly 

 referred to. 



