370 THE ORIOIN OF THE OLDEST FOSSILS. 



directly upon the floating organisms for food, it is not probable that 

 they first established themselves in shallow water, where the food sup- 

 l)ly is botli scanty and mixed with sediment; nor is it probable that 

 their establishment Mas delayed until the great depths had become 

 favorable to life. 



The belts around elevated areas far enough from shore to be free 

 from sediment, and deep enough to permit the pelagic fauna to reach 

 its fnll development above them, are the most favorable spots, and 

 paleontological evidence shows that they were seized upon very early 

 in the history of life on the bottom. 



It is probable that colony after colony was establishe<l on the bottom 

 and afterwards swept away by geological change like a cloud before 

 the wind, and that the bottom fauna Avhich we know was not the first. 

 Colonies which started in shallow water were exposed to accidents from 

 M'hich those in great depths were free; and in view of onr knowledge of 

 the permanency of the sea floor and of the broad outlines of the conti- 

 uents, it is not impossible that the first fauna which became established 

 in the deep zone around the continents may have persisted and given 

 rise to modern animals. However this may be, we must regard this 

 deep zone as the birthplace of the fauua which has survived, as the 

 ancestral home ot all the improved metazoa. 



The effect of life upon the bottom is more interesting than the place 

 where it began, and we are uow to consider its infinence upon animals,, 

 all whose ancestors and competitors and enemies had previously been 

 pelagic. The cold, dark, silent, quiet depths of the sea are monotonous 

 compared with the land, but they introdnced many new factors iuto' 

 the course of organic evolution. 



It is doubtful whether the animals which first" settled on the bottom 

 secured any more food than floating ones, but they undoubtedly obtained 

 it with less ettbrt, and were able to devote their suj)erfluous energy to 

 growth and to multiplication, and thus to become larger and to increase 

 in numbers faster than pelagic animals. Their sedentary life must have 

 been favorable to both sexual and asexual multiplication, and the tend- 

 ency to increase by budding must have been quickly rendered more 

 active, aud one of the first results of life on the bottom must have been 

 to promote the teudency to form connected cormi, aud to retain the cou- 

 uection between the i)areut aud the bud until the latter was able to 

 obtain its own food and to care for itself The animals which first 

 acquired the habit of resting on the bottom soon began to multiply 

 faster than their swimming allies, and their asexually produced progeny, 

 remaining for a longer time attached to and nourished by the parent 

 stock, were much more favorably placed for rapid growth. As the 

 animals of the bottom live on a surface, or at least a thin stratum, 

 while swimming animals are distributed through solid space, the rapid 

 multiplication of bottom animals must soon have led to crowding and 

 to competition, aud it quickly became harder and harder for new forms 



