THE ORIGIN OF THE OLDEST FOSSILS, ETC. 283 



is both scanty and mixed with sediment ; nor is it probable 

 that their estabUshment was delayed until the great depths had 

 become favourable 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 full development above them, are the most favourable 

 spots, and palaeontological 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 established on the 

 bottom, and afterwards swept away by geological change like a 

 cloud before the wind, and that the bottom fauna which we know 

 was not the first. Colonies which started in shallow water were 

 exposed to accidents from which those in great depths were free ; 

 and in view of our knowledge of the permanency of the sea-floor 

 and of the broad outlines of the continents, it is now 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 fauna which has survived ; as the ancestral 

 home of all the improved metazoa. 



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

 place where it began, and we are now to consider its influence 

 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 

 introduced many new factors into 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 undoubt- 

 edly obtained it with less effort, and were able to devote their 

 superfluous energy to growth and to multiplication, and thus to 

 become larger and to increase in numbers faster than pelagic ani- 

 mals. Their sedentary life must have been favourable to both 

 sexual and asexual multiplication, and the tendency to increase by 

 budding must have been quickly rendered more active, and one of 

 the first results of life on the bottom must have been to promote 

 the tendency to form connected cormi, and to retain the connection 

 between the parent and the bud until the latter was able to obtain 

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



