418 THE INHABITANTS OF THE SEA. 



sufficient to put any idea of life out of the question ? There 

 was a curious popular notion that on descending deeper and 

 deeper the ' sea water became gradually, under the pressure, 

 heavier and heavier, so that at last it became more weighty than 

 molten gold. But water is, in fact, almost incompressible ; so 

 that its density at 2,000 fathoms is scarcely appreciably in- 

 creased. Any free air suspended in the water, or contained in 

 any compressible tissue of an animal at 2,000 fathoms, would 

 of course be reduced to a mere fraction of its bulk ; but the 

 animals subject to the pressure of the deep seas, being permeated 

 throughout their whole organisation by incompressible fluids at 

 the same pressure, are consequently as capable of bearing it as 

 we do the pressure of the atmosphere. The absence of light 

 seemed another circumstance incompatible with the existence 

 of animal life at abyssal depths, as all plants depend upon 

 light for their growth, and their absence apparently involves 

 that of vegetable food, which, as we all know, forms everywhere 

 the substratum of animal existence. We have as yet very little 

 exact knowledge as to the distance to which the sun's light 

 penetrates into the water of the sea. According to some recent 

 experiments it would appear that the rays capable of affecting 

 a delicate photographic film are very rapidly cut off, their effect 

 being imperceptible at the depth of only a few fathoms ; and 

 though probably some portions of the sun's light possessing 

 certain properties may penetrate to a much greater distance, it 

 is certain that, beyond the first fifty fathoms, plants to whose 

 existence light is essential are barely represented, and after two 

 hundred fathoms entirely absent. 



But though plant-life is thus limited to the more superficial 

 parts of the ocean, the analysis of sea water, taken in all 

 localities and at all depths, has shown that it everywhere 

 contains a very appreciable and very uniform quantity of 

 organic matter in solution and in suspension. It is thus 

 quite intelligible that numberless protozoa — whose distinctive 

 character is that they are capable of being supported by the 

 absorption of organic matter through the surface of then- 

 bodies — are able to exist in the dark abysses of the sea, and in 

 their turn afford nourishment to more highly organised animals. 



After these general remarks on the creatures of the deep, 

 I will now give a brief account of their various groups. 



