chap, i.] INTRODUCTION. 47 



matter, in solution and in suspension. Its sources 

 are obvious. All rivers contain a considerable quan- 

 tity. Every shore is surrounded by a fringe which 

 averages a mile in width, of olive and red sea- 

 weed. In the middle of the Atlantic there is a 

 marine prairie, the ' Sargasso sea,' extending over 

 three millions of square miles. The sea is full of 

 animals, which are constantly dying and decay- 

 ing. The amount of organic matter derived from 

 these and other sources by the water of the ocean 

 is very appreciable. Careful analyses of the water 

 were made during the several cruises of the ' Porcu- 

 pine ' to detect it and to determine its amount, 

 and the quantity everywhere was capable of being 

 rendered manifest and estimated, and the propor- 

 tion was found to be very uniform in all localities 

 and at all depths. Nearly all the animals at extreme 

 depths — practically all the animals, for the small num- 

 ber of higher forms feed upon these — belong to one 

 sub-kingdom, the Protozoa ; whose distinctive charac- 

 ter is that they have no special organs of nutrition, 

 but absorb nourishment through the whole surface 

 of their jelly-like bodies. Most of these animals 

 secrete exquisitely formed skeletons, some of silica, 

 some of carbonate of lime. There is no doubt that 

 they extract both these substances from the sea- 

 water; and it seems more than probable that the 

 organic matter which forms their soft parts is 

 derived from the same source. It is thus quite 

 intelligible that a world of animals may live in 

 these dark abysses, but it is a necessary condition 

 that they must chiefly belong to a class capable of 

 being supported by absorption through the surface 



