280 THE ORIGIN OF THE OLDEST FOSSILS, ETC. 



source of food for all the inhabitants of the ocean. The supply 

 is primeval as well as inexhaustible, and all the life of the ocean 

 has gradually taken shape in direct dependence upon it. In view 

 of these facts, we cannot but be profoundly impressed by the 

 thought that all the highly organised marine animals are products 

 of the bottom or the shore or the land, and that while the largest 

 animals on earth are pelagic, the few which are primitively pelagic 

 are small and simple. 



The reason is obvious. The conditions of life at the surface 

 are so easy that there is little fierce competition, and the inorganic 

 environment is so simple that there is little chance for diversity 

 of habits. 



The growth of terrestrial plants is limited by the scarcity of 

 food, but there is no such limit to the growth of pelagic plants or 

 the animals which feed on them, and while the balance of life is 

 no doubt adjusted by competition for food this is never very fierce, 

 even at the present day, when the ocean swarms with highly orga- 

 nised wanderers from the bottom and the shore. Even now the 

 destruction or escape of a microscopic pelagic organism depends 

 upon the accidental proximity or remotenesses of an enemy rather 

 than upon defence or protection, and survival is determined by 

 space relations rather than a struggle for existence. 



The abundance of food is shown by the ease with which wan- 

 derers from the land, like sea birds, find places for themselves in 

 the ocean, and the rapidity with which they spread over its 

 whole extent. 



As a marine animal the insect, Halobates, must be very mod- 

 ern as compared with most pelagic forms, yet it has spread over 

 all tropical and sub-tropical seas, and it may always be found 

 skimming over the surface of mid-ocean as much at home as a 

 Gerris in a pond. I never found it absent in the Gulf Stream 

 when conditions were favourable for collecting. 



The easy character of pelagic life is shown by the fact that 

 the larvse of innumerable animals from the bottom and the 

 shore have retained their pelagic habit, and I shall soon give 

 reasons for believing that the larva of a shore animal is safer 

 at sea than near the shore. 



There was little opportunity in the primitive pelagic fauna and 



