170 JOHNS HOPKINS UNIVERSITY MORPHOLOGICAL MONOGRAPHS. 



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 them- 

 selves. 



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 influence 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 fragmentary 

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

 may thrive with the dense luxuriance of tropical vegetation, 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. 



While 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 bottom in nearly a mile of water, several of the 

 hooks dropped into the mouths of large sea anemones, so that they were 

 brought up uninjured, and were carried more than three hundred miles 

 to the laboratory, where they lived for some time in an aquarium. 



The number of remains of palaeozoic crinoids and brachiopods and 

 trilobites which are crowded into a slab of fine-grained limestone is most 

 astounding, and it testifies most vividly and forcibly to the wealth of life 

 on the old sea-floor. 



