262 ANIMALS OF THE SEA FLOOR 



origin unknown, it could be said without hesitation to 

 be an inhabitant of the abyss. 



The physical conditions prevailing over the bottom 

 of the deep sea are almost uniform, so far as we can 

 perceive, through long periods of time and throughout 

 all oceans. The darkness is absolute, or broken only 

 by gleams of light from " phosphorescent" animals. 

 The temperature is very low, at most 3 or 4 F. above 

 freezing, and constant. The pressure is enormous, 

 upwards of 3 tons per square inch at a depth of 3,000 

 fathoms. It is hardly necessary to point out that, 

 once the tissues of an organism were adjusted to meet 

 this pressure, it would be felt no more than is the 

 pressure of the atmosphere by the inhabitants of the 

 earth's surface. The effect of this pressure, combined 

 with the low temperature, on the metabolism of the 

 animal (the chemical changes connected with its vital 

 processes) must, however, be very great. The water 

 above the bottom is still or in very slow movement 

 (unless, perhaps, in some narrow straits), and is not 

 rendered turbid by any river sediment or by mud 

 stirred up by currents from the bottom. The bottom 

 itself is covered with a fine ooze, usually without 

 rocks or other solid bodies to afford support to seden- 

 tary organisms. In the absence of any vegetable 

 growth the inhabitants of the deep sea must be car- 

 nivorous, and as it is not possible for them to sustain 

 life by feeding mutually on each other, we must look 

 for some external source of supply. This is to be 

 found in the constant rain of dead organisms which 

 have lived and perished in the upper layers of the 

 ocean. The existence of this constant supply of 

 organic matter is illustrated by the fact that the 

 oozes which cover the ocean bed over a large part of 

 its extent (Chapter VI.), are formed from the shells 



