THE SEA FISHERIES OF EASTERN NORTH AMERICA. 73 



the extremely minute and more or less microscopic form of diatoms. 

 These, however, swarm infill 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 tlie 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 alg?e 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 a rich 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-turtles 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 plants very few species are known in the ocean 

 (iudeed 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 auimals 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 oHLimnotia 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 



