346 ANNUAL OF SCIENTIFIC DISCOVERY. 



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 limi- 

 tation 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 

 sensorial apparatus, susceptible to the influence of light. 



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 prob- 

 lem. But it is almost certain that a limit is attained, and that, more- 

 over, long before the deep recesses gauged by the sounding machine 

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

 trate, even in its most attenuated condition ; and yet, as shall here- 

 after be shown, creatures have been found down in those profound and 

 dark abysses whose coloring 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 

 undoubtedly a highly important one, I hope to be able to prove that 

 it is not of essential value, as has heretofore been laid down, in 

 determining the final issue of animal life in the sea. 



It is almost needless to state that, at the sea level, there exists a 

 pressure of fifteen pounds on every square inch of surface, due to the 

 weight of the atmospheric column resting upon it ; and that the pres- 

 sure on the successive strata of water in the sea, as the depth in- 

 creases, is infinitely in excess of this, inasmuch as a column of water 

 only thirty-three feet in height is capable of counterbalancing the 

 entire atmospheric column, which extends to a height of about forty- 

 five miles. Accordingly, for every thirty-three feet of descent in the 

 sea, putting out of consideration the effect of the superincumbent col- 

 umn in actually diminishing the bulk of the portions beneath by aug- 

 menting their density, there is an additional fifteen pounds. At great 

 depths, therefore, the aggregate pressure becomes stupendous. As is 

 well known, pieces of light wood let down to a depth of fifteen hun- 

 dred or two thousand fathoms become so compressed and surcharged 

 with water as to be too heavy to float. But there is a fallacy in this 

 experiment ; for the contraction of the woody fibre and cells is a 

 necessary consequence of their submission to an amount of pressure 

 so enormously in excess of that under which they originated. With 

 organisms which have been developed, from first to last, under the 

 full operation of any given amount of pressure, the result would not be 

 of this nature ; for the equalization of the pressure, within and with- 

 out their entire structure, although it might possibly exercise some 

 definite effect in determining their shape, size, or even functions, 

 cannot, I submit, operate in causing the creatures living under it to 

 experience any more detrimental results than we experience from 

 the fifteen pounds on every square inch, or about fourteen tons on 

 the general surface of our bodies, near the sea level. 



It can scarcely be wondered at, that, under such apparently extra- 

 ordinary conditions, the maintenance of life, even in its least devel- 

 oped aspect, should have been deemed absolutely impossible at ex- 



