CHAP. 1.] INTRODUCTION. AZ 
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 ‘ Por- 
cupine’ 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 
number of higher forms feed upon these—belong to 
one sub-kingdom, the Protozoa; whose distinctive cha- 
racter 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 
