1861.] on Animal Life at vast Depths in the Ocean. 301 



can only extend to a limited depth, unless, as has been assumed by 

 some of our highest authorities, the lower strata of sea water, being 

 subject to increased pressure, become capable of holding in solution a 

 greater quantity of oxygen ; and, by robbing the superincumbent 

 strata of that which they contain, gradually become saturated with it. 

 Should this view be correct, there must be a point at which the maxi- 

 mum amount of oxygen which sea water can absorb, is permanently 

 present in it. But, inasmuch as the vegetable cell, simple though it 

 be in structure, can eliminate carbon from the medium in which it 

 lives, it is not unreasonable to assume that the lowest forms of animal 

 life, even where no specialized organs are traceable, may, in like man- 

 ner, be able to eliminate oxygen directly from the water around them. 



The temperature of the sea is materially influenced by the climatic 

 conditions of different latitudes ; and, of course, exercises a powerful 

 effect both on the distribution and abundance of the higher orders of 

 living beings present in its waters. But, as has been shown, this 

 influence is not manifest, or at all events, not so manifest in the lower 

 orders ; for at great depths the variability of the temperature is 

 reduced within very narrow limits in all latitudes. Now the higher 

 orders of oceanic creatures inhabit only the surface waters, never 

 sinking down to extreme depths. In the case of some of the lower 

 forms, on the other hand, a very extended pathymetrical range exists, 

 putting out of the question those which constantly dwell on the sea 

 bed itself, of which I shall presently have to speak. 



In like manner. Light, or rather the absence of it, can hardly be 

 said to determine, in any important degree, the distribution and limita- 

 tion of the lower forms of animal life. Light is not essential even in 

 the case of some of the higher orders. A large class of creatures, 

 both terrestrial and marine, possess no true organs of vision, although 

 there is good reason for believing that they do possess some special 

 sensory apparatus, susceptible to the influence of light ; whilst certain 

 creatures, whose habitation is in subterranean caves or lakes, as in 

 the Magdalena caves near Adelsberg, and the Great Mammoth caves 

 in Kentucky, either possess no organs of vision, or possess them in so 

 rudimentary a state, as to prove clearly that the absence or imperfect 

 development of this sense may be compensated for by the higher 

 development of other senses. 



It is impossible at present to say to what depth light penetrates 

 in the sea. The photographic art will, no doubt, one day solve the 

 problem. But it is almost certain that a limit is attained, and that, 

 moreover, long before the deep recesses gauged by the sounding 

 machine are reached, where the light-giving portion of the ray cannot 

 penetrate, even in its most attenuated condition ; and yet, as shall 

 hereafter be shown, creatures have been found down in those profound 

 and dark abysses, whose colouring is as delicate and varied as if they 

 had passed their existence under the bright influence of a summer 

 sun ! 



Pressure is the last condition which has to be noticed. Although 



