368 THE ORIOxIN OF THE OLDEST FOSSILS. 



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 i)resent 

 day, when the ocean swarms with highly organized wanderers from 

 the bottom and the shore. Even now the destruction or escape of a 

 microscopic pelagic oiganism depends upon the accidental proximity 

 or remoteness of an enemy rather than upon defense or i)rotection, and 

 survival is determined by space relations rather than a struggle for 

 existence. 



The abundance of food is shown by the ease with which wanderers 

 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 modern as 

 compared with most pelagic forms, yet it has spread over all tropical 

 and subtropical seas, and it may always be found skimming over the 

 surface of mid-ocean as nuich at home as a Gerris in a pond. I never 

 found it absent in the Gulf Stream Avhen conditions were favorable for 

 collecting. 



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

 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 i)elagic fauna and flora 

 for an organism to gain superiority by seizing upon an advantageous 

 site or by acquiring peculiar habits, for one place was like another, and 

 peculiar habits could count for little in comparison with accidental 

 space relations. After the fauna of the surface had been enriched by 

 all the marine animals which have become secondarily adapted to 

 pelagic life, competition wath those improved forms brought about 

 improvements in those which were strictly pelagic in origin, like the 

 siphonophores, and those wanderers li^om the bottom introduced another 

 factor into the evolution of pelagic life, for their bodies have been 

 utilized for jirotection or concealment and in other ways, and we now 

 have fishes which hide in the poison curtain of Physalia, Crustacea 

 which live in the pharynx of Salpa or in the mouth of the menhaden, 

 barnacles and sucking fish fastened to whales and turtles, besides a 

 host of external and internal parasites. The primitive ocean furnished 

 no such opportunity, and the conditions of pelagic life must at first 

 have been very simple, and while competition Avas not entirely absent 

 the i)ossibilities of evolution must have been extremely limited and 

 the progress of divergent modification very slow so long as all life was 

 restricted to the waters of the ocean. 



There can be no doubt that floating life was abundant for a long 

 period when tlie bottom was uninhabited. The slow geological cbanges 

 by which tlie earth gradually assumed its present character present a 

 boundless field for speculation, but there can be no doubt that the sur- 

 face of the primeval ocean became, fit for living things long before the 



