NATURAL selection; AND THE ANTIQUITY OF LIFE 227 



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

 conditions were favorable for collecting. 



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

 the larvae 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 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 compari- 

 son with accidental space relations. After the fauna of the sur- 

 face had been enriched by all the marine animals which have 

 become secondarily adapted to pelagic life, competition with those 

 improved forms brought about improvements in those which were 

 strictly pelagic in origin, like the siphonophores, and those wan- 

 derers from the bottom introduced another factor into the evolu- 

 tion of pelagic life, for their bodies have been utilized for protection 

 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 exter- 

 nal 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 was not entirely absent 

 the possibilities 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 the bottom was uninhabited. The slow geologi- 

 cal changes by which the earth gradually assumed its present 

 character present a boundless field for speculation, but there can 

 be no doubt that the surface of the primeval ocean became fit for 

 living things long before the deeper waters or the sea-floor, and 

 during this period the proper conditions for the production of 

 large and complicated organisms did not exist, and even after the 

 total amount of life had become very great it must have consisted 

 of organisms of small size and simple structure. 



