THE FISH OF THE DEEP SEA 153 



It would at least be interesting to know if this 

 dark coloration of the mucous membranes is in any 

 way correlated with any modification of the structure 

 or function of the kidneys. At present we have no 

 recorded observations on this point, but it is to be 

 hoped that, when we have a sufficient number of 

 specimens brought home from the deep water, a 

 systematic investigation of this subject will be made. 



Lastly, it should be pointed out that our know- 

 ledge of the abysmal fauna has not, at present, brought 

 to light any evidence that the fish are of an extra- 

 ordinarily large size. In many groups of animals, as 

 I have frequently pointed out in the last few chapters, 

 the large and gigantic species or specimens are only 

 found in the abyss. This may also be the case with 

 fishes, but we have no evidence that it is so. The 

 only methods that have been used at present for the 

 investigation of the fauna living on or near the 

 floor of the deep oceans, are not of a kind to lead 

 to the capture of really large fish. That they may 

 exist is highly probable, but all that we know at 

 present is, that the fish with which we are acquainted 

 living at great depths are not in any way remarkable 

 for their great size. 



Of the only two Elasrnobranchs, one, namely Raia 



