464 THE JOURNAL OF GEOLOGY. 



that he met with such enormous masses of Limacina to the 

 northwest of Scotland, that each bucket of water contained 

 thousands. 



The tendency to gather in crowds is not restricted to the 

 smaller 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, and we are told of one school 

 which was a windrow of fish half a mile wide and at least 

 twenty miles long. But while pigeons are plant eaters, the 

 mackerel are rapacious hunters, pursuing and devouring the her- 

 rings as well as other animals. 



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

 solid wall. In 1879 three hundred thousand river herring were 

 landed in a single haul of the seine in Albemarle Sound ; but 

 the herring are also carnivorous, each one consuming myriads 

 of copepods every day. 



In spite of this destruction and the ravages of armies of 

 medusae and siphonophores and pteropods the fertility of the 

 copepods is so great that thev are abundant in all parts of the 

 ocean, and they are met with in numbers which exceed our 

 power 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 sur- 

 face, and that the banks of copepods are sometimes more than a 

 mile thick. When we reflect that thousands would find ample 

 room and food in a pint of water, one can form some faint con- 

 ception of their universal abundance. 



The organisms which are visible in the water of the ocean 

 and on the sea bottom are almost universally engaged in devour- 

 ing each other, and many of them, like the blue-fish, are never 

 satisfied with slaughter, but kill for mere sport. 



Insatiable rapacity must end in extermination unless there is 

 some unfailing supply, and as we find no visible supply in the 



