LIMITATION OF FAMILIES 117 



seals ; sea-elephants and walruses live on shell-fish ; whales, 

 dolphins and porpoises all live on sea-animals, and many of them 

 are fierce beasts of prey. Most fishes are carnivorous, and one 

 has only to think of the shoals of herring and mackerel, the wall- 

 like masses of codfish and the great hauls of sardines to realise the 

 enormous animal-eating population of the sea. Most of the lower 

 forms of life are carnivorous. The gardens of the tropic island 

 sea-bottoms, with their brilliantly coloured, flower-like polyps, are 

 composed of animals that live on other animals almost exclusively. 



A small portion of the ultimate food-supply of the sea consists 

 of the flotsam and jetsam from the land, of waste matter washed 

 down by the great rivers. But the main source is to be found 

 in the sea- water itself. If the open sea seems at first a barren waste, 

 the tow-net shows that it contains myriads of small animals. 

 These are the larvae of innumerable creatures that live on the shore 

 or on the bottom, together with countless wanderers that have no 

 fixed abode, but drift all their lives with the ocean currents. 

 Amongst them are great numbers of small plants, like the 

 protococci that form the green scum on pools of rain-water, or the 

 diatoms familiar to every one who uses a microscope. These, in 

 the fashion of terrestrial green plants, build up food-material from 

 the inorganic salts in the sea and from the gases of the air. Little 

 animals live on them and are in turn fed on by larger animals. In 

 the depths of the ocean, where no light penetrates, green plants 

 cannot live, and the food-supply must be derived from live or dead 

 animals that rain down from the surface. 



And so on land and in the sea, in the air and in the waters, living 

 creatures are ceaselessly devouring other living creatures, and the 

 feeble and succulent young are the readiest victims. The more 

 powerful carnivorous animals seem to rejoice in their strength 

 and skill, and many of them destroy far more victims than they 

 require for food. Others are extremely voracious, and appear to 

 have no limit to their capacity for digestion or to their appetite. 

 If we reflect on the dangers from accident, disease and the host of 

 hungry enemies, the wonder seems to be, not that species occasionally 

 have become extinct, but that any have maintained their existence. 



The most common device in the animal kingdom to meet the 

 immense destruction of life is for the young to be produced in 

 enormous quantities. In the sea especially, where most animals 

 are carnivorous, the ripe females are bloated with a great burden 

 of eggs, to be counted by millions or thousands or hundreds, and 



