276 THE ORIGIN OF THE OLDEST FOSSILS, ETC. 



In the Chesapeake Bay the sheepshead browses among the 

 algae upon the submerged rocks and piles like a marine sheep, but 

 its food is exclusively animal, and I have lain upon the edge of a 

 wharf watching it crunch the barnacles and young oysters until the 

 juices of their bodies streamed out of the angles of its mouth, 

 and gathered a host of small fishes to snatch the fragments as they 

 drifted away with the tide. 



Many important fishes, like the cod, pasture on the bottom, but 

 their pasturage consists of molluscs and annelids and Crustacea 

 instead of plants, and the vast majority of sea fishes are fierce 

 hunters, pursuing and destroying smaller fishes, and often exhibit- 

 ing an insatiable love of slaughter, like our own blue fish and the 

 tropical albacore and barracuda. Others, such as the herring, feed 

 upon smaller fishes and the pelagic pteropods and copepods ; and 

 others, like the shad, upon the minute organisms of the ocean ; 

 but all, with few exceptions, are carnivorous. In the other great 

 groups of marine animals we find some scavengers, some which 

 feed upon micro-organisms, and others which hunt and destroy 

 each other; but there is no group of marine animals which cor- 

 responds to the herbivora and rodents and the plant-eating birds 

 and insects of the land. 



There is so much room in the vast spaces of the ocean, and so 

 much of it is hidden, that it is only when surface animals are 

 gathered together that the abundance of marine life becomes 

 visible and impressive ; but some faint conception of the boundless 

 wealth of the ocean may be gained by observing the quickness 

 with which marine animals become crowded together at the surface 

 in favourable weather. On a cruise of more than two weeks along 

 the edge of the gulf-stream, I was surrounded continually night 

 and day by a vast army of dark brown jelly-fish (Linerges mercutia), 

 whose dark colour made them very conspicuous in the clear water. 

 We could see them at a distance from the vessel, and at noon when 

 the sun was overhead we could look down to a great depth through 

 the centre-board well, and everywhere, to a depth of fifty or sixty 

 feet, we could see them drifting by in a steady procession, like 

 motes in a sunbeam. We cruised through them for more than five 

 hundred miles, and we tacked back and forth over a breadth of 

 almost a hundred miles, and found them everywhere in such 



