34 ANIMAL COLOEATION. 



layer of living organisms ni^on the actual surface of the sea, 

 but extend downwards to some depth ; hence it follows that 

 light coming from above must be greatly prevented from 

 passing through the surface water by the innumerable spots in 

 the otherwise transparent organisms. 



Near to the shores of continents the opacity of the ocean 

 waters is increased by the presence of sediment washed down 

 by rivers or by rain and carried far out to sea by rivers and by 

 the movements of the sea water itself. Such sediment occurs 

 at as great a distance as two hundred miles from the shore ; 

 but it is, of course, more abundant as continental land is 

 approached. In any case, the total absence of chlorophyll- 

 bearing plants from abyssal depths seems to point to an 

 absence of light ; for chlorophyll, with a few exceptions, is 

 not produced in darkness. 



It may be, therefore, admitted, in agreement with the 

 opinion of most persons, that the ocean abysses are profoundly 

 dark. 



One of the most noteworthy discoveries in view of this fact 

 was the occasional, in some groups of deep-sea animals usual, 

 occurrence of eyes. This discovery led to the formulation of 

 the celebrated theory of abyssal light, which was first put 

 forward by the late Dr. W. B. Carpenter and strongly supported 

 by Sir Wyville Thomson. This theory accounted for the 

 presence of eyes, on the view that the phosphorescence of deep- 

 sea organisms furnished the requisite light to render the eyes 

 available. That phosphorescence is a common phenomenon 

 among deep-sea animals is an undoubted fact ; it occurs 

 among representatives of the most diverse classes : Crustaceans, 

 Alcyonarians, Hydroids, Fishes and other groups are often 

 phosphorescent. 



The light is sometimes remarkably intense : Professor 



