162 W. K. BROOKS. 



of a capacity for budding, and it is not at all improbable that 

 the primitive pelagic metazoa multiplied by buds ; although 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, was a result, and probably one 

 of the first results, of life on the bottom. 



The animals which first acquired the habit of resting upon the 

 bottom therefore soon began to multiply faster, both sexually and 

 asexually, than their swimming allies ; and their asexual progeny 

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

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

 bottom animals 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, and it soon 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 repre- 

 sented among the modern metazoa is therefore what we should 

 expect, for after the foundation for the fauna of the bottom was 

 laid it became, and ever afterwards remained, difficult for new 

 forms to establish themselves. 



Our knowledge of the sea-bottom is for the most part from three 

 sources : from dredgings and other methods of exploration ; from 

 rocks which were originally laid down beyond the immediate in- 

 fluence of the continents, and from the patches of the bottom fauna 

 which have been gradually brought near its surface by the growth 

 of coral reefs ; and from all these sources we find testimony to the 

 density of the crowd of animals on favorable spots. 



Deep-sea exploration can give only the most scanty and frag- 

 mentary basis for a picture of the sea-bottom, but it shows that its 

 animal life may thrive with the dense luxuriance of tropical vege- 

 tation, and Sir William Thomson says that he once brought up at 

 one time on a " tangle," which was fastened to a dredge, over 20,000 

 specimens of a single species of sea-urchin. 



AVhile cruising on the U. S. Fish Commission schooner Grampus, 

 I was interested to find that when a ground-line with baited fish- 

 hooks had been sunk to the l)ottom in nearlv a mile of water, several 



