136 W. K. BROOKS. 



and banks of pteropods (Clio and Limacina), so dense that they 

 seem almost solid, are met even beyond the arctic circle. 



Haeckel says that in a cruise to the northwest of Scotland he met 

 with such enormous masses of Limacina that each bucket of water 

 which was dipped up contained thousands. 



The tendency to gather in crowds is not restricted to the smaller 

 pelagic animals, and many species of raptorial fishes are found in 

 densely packed banks. 



The fishes in a school of mackerel are as numerous as the birds 

 in a flight of wild pigeons. Goode, in his History of Aquatic 

 Animals, tells of one school of mackeral which was estimated to 

 contain a million barrels, and of another which was a windrow of 

 fish half a mile wide and at least twenty miles long ; but while the 

 pigeons are plant-eaters, the mackerel are rapacious hunters, pur- 

 suing and devouring the herrings, as well as the pteropods and 

 pelagic Crustacea. 



Herring swarm like locusts, and a herring bank is almost a solid 

 wall. In 1879 three hundred thousand river herring were landed 

 by a single haul of the seine in Albemarle Sound ; but the herrings 

 are also carnivorous, each one consuming myriads of copepods every 

 day. In spite of this destruction and the ravages of armies of me- 

 dusae and siphonophores and pteropods, the fertility of the copepods is 

 so great that they are abundant in all parts of the ocean, and they are 

 met with in numbers which exceed our powers of comprehension. 



On one occasion the Challenger steamed for two days through a 

 dense cloud formed of a single species, and they are found in all 

 latitudes from the arctic regions to the equator, in masses which 

 discolor the water for miles. We know, too, that they are not 

 restricted to the surface, and that the banks of copepods are some- 

 times a mile thick. When we reflect that thousands M'ould find 

 ample room and food in a pint of water, we can form some faint 

 conception of their universal abundance. 



The Peimary Food-supply. 



As the result of our review, we find that the organisms which 

 are visible without a microscope in the water of the ocean and on 

 the sea bottom are almost universally engaged in devouring each 



