ANIMAL LIFE 183 



number of species represented by single 

 specimens is quite remarkable. 



The sixth column in the table shows the 

 large number of genera in relation to the 

 number of species in the hauls from the deeper 

 zones ; in fact the ratio of genera to species 

 rises in a most regular manner on proceeding 

 into deeper and deeper water and farther and 

 farther from land. In the deepest zone the 

 species stand to the genera in the ratio of 

 5 to 4, while in the shallowest zone the 

 ratio is 3 to 1. This relation might be 

 explained by supposing that the deep sea 

 was peopled by continuous migrations from 

 the mud-line downwards and seawards at 

 many different periods of time and from 

 many different parts of the world. 



In some instances the variety of animals 

 brought up in the trawl and dredge from 

 deep water was much greater than in similar 

 hauls in shallow water. This was especially 

 the case in the deep water of the Kerguelen 

 region of the Southern Ocean, where the 

 " Challenger " took eight hauls in depths 

 between 1260 and 2600 fathoms yielding a 

 total of 272 species, or an average of 34 species 

 per haul ; at one station in 1600 fathoms 

 about 200 individuals belonging to 89 species 

 were procured. This profusion of life in the 

 Southern Ocean may be accounted for by 



