ANIMAL LIFE 181 



versal, the polar forms to be widely distributed, 

 and the development generally direct ; with 

 an increase of heat at the equator there would 

 be a great development of new genera and 

 species having pelagic larval stages within the 

 tropics, while polar organisms would evolve 

 much more slowly. 



Bathy metrical Distribution of the Benthos. — 

 In discussing briefly the distribution of the 

 benthos we may base our remarks on the 

 results of the " Challenger " Expedition, 

 deduced from dredgings and trawlings taken 

 in deep and shallow water in all parts of the 

 world under practically uniform conditions. 

 These results are set forth in the table on 

 page 182, indicating the number of species and 

 genera of fishes and invertebrates (excluding 

 protozoa) recorded in the "Challenger" 

 Reports from the various dredging and trawling 

 stations, arranged in zones of depth. 



In this table the number of individual 

 specimens from the shallow-water zone in 

 depths less than 100 fathoms is left blank, 

 because of the difficulty in arriving at an 

 estimate of the numbers captured. In strik- 

 ing contrast to the abundance. of individuals 

 in shallow water is the fact that in deep 

 water beyond 1000 fathoms the " Challenger " 

 rarely took more than three or four specimens 

 of any one species in each haul, and the 



