128 
CRITICAL EPISODE IN EVOLUTION 
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. 
In view of our knowledge of the permanency of the sea-floor and 
of the broad, outlines of the continents, 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 birth¬ 
place 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 of whose ancestors and competitors and enemies 
had been previously 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 un¬ 
doubtedly obtained it with less effort, and were able to devote 
their superfluous energy to growth and to multiplication, and 
thus become larger and increased 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 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 on the bottom live on the surface, or 
at least in 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, and it quickly 
became harder and harder for new forms from the open water 
