
THE SEA FISHERIES OF EASTERN NORTH AMERICA. 73 
the extremely minute and more or less microscopic form of diatoms, 
These, however, swarm in all portions of the ocean and extend into its 
uttermost ramifications, occurring at depths of three or four thousand 
fathoms, or at the surface, and equally abundant in the middle of the 
ocean as on its shores. 
There appears to be an immense variety of the lower order of animals, 
whose special function it is to assimilate these minute alge and convert 
them into animal matter. These, in turn, are devoured by animals of a 
higher organization or of larger dimensions, although still microscopic; 
and after a time, by a succession of such transformations, the matter 
becomes a portion of the organism of the larger mollusks, crustaceans, 
radiates, worms, or vertebrates. 
The larger plant-growths in the sea also have similar relationships, 
the so-called sea-weeds, sea-mosses, kelp, &c., furnishing arich variety 
of food. Various mollusks and crustaceans devour both the living sea- 
weed and the dead with avidity. The Nereis and others among the 
worms, too, will consume decaying vegetable matter. 
The great sea-turtlés are also believed to depend very largely upon 
sea-weeds for food, and the manatee or sea-cow of tropical and sub-trop- 
ical regions also feeds upon sea-weeds and other submerged marine veg: 
etables. 
There are comparatively few fishes within our knowledge that cer- 
tainly eat sea-weed as a portion of their food, although it is said that 
the stomach of the striped bass frequently contains such quantities of 
ulva and other succulent vegetation as to render it almost certain that 
it must have taken it as an article of food. Not unfrequently the vege- 
table contents of the stomachs of certain fishes may have been taken 
in accidentally in connection with some shrimp or mollusk which was 
resting upon it at the time of capture. 
Of the higher order of ptants very few species are known in the ocean 
(indeed the Zostera or eel-grass is said to be the only form), but immense 
quantities of the trunks of trees, &c., are constantly carried into the 
sea from the rivers, and are very speedily attacked by animals specially 
appointed for the purpose, the most familiar being the teredo or ship- 
worm, and sometimes certain shrimps or crustaceans, the best known of 
which on our coast are species of Limnoria and Chelura. These very soon 
perform their part in honeycombing and reducing to minute fragments 
vegetable matter of whatever magnitude, and the fragments, after being 
made too small to serve as burrows, become in this finally divided state 
food for other marine objects. 
The echini, so abundant on our coast, and especially in the northern 
waters, are quite omnivorous in their habits and consume both animal 
and vegetable substances, and are apparently especialy adapted for 
those of harder texture. They devour greedily the soft portions as well 
as the bones of fishes and possibly of other vertebrates, and have been 
known to eat off the bark from the stakes used in constructing the 
