PKOTOZOA, CCELENTERA, AND ECHINODEEMA 87 



that the hopes and wishes of these naturalists were 

 really justified. Although thousands of species of 

 animals have been described in the volumes that 

 have been devoted to deep-sea work, the number of 

 the sub-kingdoms and classes remains the same, 

 and indeed the number of new families and genera 

 has not been increased in any very unprecedented 

 manner. 



We have found no animals in the depths of the 

 sea of such interest and importance as Ornitho- 

 rhynchus, Amphioxus, Balanoglossus, Peripatus, 

 Millepora, or Yolvox among the living, or Hipparion, 

 Archseopteryx, Ammonites, Slimonia, and the Trilo- 

 bites among extinct animals. 



The abysmal fauna is not in fact remarkable for 

 possessing a large number of primitive or archaic 

 forms. It is mainly composed of a number of species 

 belonging to the families and genera of our shallow- 

 water fauna that have, from time to time, migrated 

 into greater depths and become modified in their 

 structure in accordance with the extraordinary con- 

 ditions of their new habitat. 



There is very good reason to believe that this 

 migration has been going on from time immemorial, 

 and consequently we find a few forms typical of the 



