THE ORIGIN OF THE OLDEST FOSSILS, ETC. 47 1 



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 evolu- 

 tion. 



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 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 

 animals. Their sedentary life must have been favorable 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 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 bot- 

 tom live on a surface, or at least a thin stratum, while swimming 

 animals are distributed through solid space, the rapid multiplica- 

 tion of bottom animals must soon have led to crowding and to 

 competition, and it quickly became harder and harder for new 

 forms from the open water to force themselves in among the old 

 ones, and colonization soon came to an end. 



The great antiquity of all the types of structure which are 

 represented among modern animals is therefore what we should 



