POPULATION OF THE SEA 97 



The Immediate conditions of aquatic life differ in many 

 Important \va}'s from those of the hind. In the hitter realm 

 the weight of the animal or plant Is not sensibly diminished 

 by the buoyancy of the air ; the result is that the creatures 

 have in all cases to dwell mainly on the ground ; even the 

 most volant of the birds and insects spend the greater part of 

 their days on the surface of the earth. The result Is that the 

 quantity of these land forms M'hich can find a place for exist- 

 ence is determined by the room afforded by a shallow zone 

 next the soil ; the depth of this stratum Is practically limited 

 between the bottom of the true soil and the top of the vegeta- 

 tion which occupies its field ; in other words, the stratum 

 occupied by organic life on the dry land Is limited In thick- 

 ness to a few score feet, and in the vast treeless regions is 

 but a foot or two in vertical extent. In the oceans, however, 

 because the greater part of the creatures may freely float or 

 swim In the water, the realm which living things can occupy is 

 vastly greater. It may extend from the surface downward to 

 the depth of four miles or more. It is true that the most 

 inhabited sections are upon or near the bottom, and within a 

 short distance of the top of the water ; yet the whole of the 

 deep is open to certain groups of beings, and probably has a 

 share of occupants. The result is that, to each square mile 

 of ocean surface, there are usually many times the number of 

 individual beings which we find in an equal area of the land. 

 As each of these creatures dies, even If it live out Its terni 

 of existence, its bodily parts are likely to become the food of 

 many hungry mouths which are exactly adapted to the task 

 of bringing its carcass back to the living state. Something of 

 this same speedy conversion of the dead to the uses of life 

 is seen upon the land ; but what we see there affords but 

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