4 THE FAUNA OF THE DEEP SEA 



reasoning, as may be seen from the following passage 

 that occurs in another part of the same book : ' It is 

 well known that marine animals are more suscep- 

 tible of change of temperature than land animals ; in- 

 deed they may be isothermally arranged with great 

 accuracy. It will, however, be difficult to get 

 naturalists to believe that these fragile creatures could 

 possibly exist at the depth of nearly 2,000 fathoms 

 below the surface ; yet as we know they can bear the 

 pressure of 1,000 fathoms, why may they not of two ? 

 We also know that several of the same species of 

 creatures inhabit the Arctic that we have fished up 

 from great depths in the Antarctic seas. The only 

 way they could get from one pole to the other must 

 have been through the tropics ; but the temperature 

 of the sea in those regions is such that they could not 

 exist in it, unless at a depth of nearly 2,000 fathoms. 

 At that depth they might ^pass from the Arctic to the 

 Antarctic Ocean without a variation of five degrees 

 of temperature ; whilst any land animal, at the most 

 favourable season, must experience a difference of 

 fifty degrees, and, if in the winter, no less than 150 

 degrees of Fahrenheit's thermometer a sufficient 

 reason why there are neither quadrupeds, nor birds, 

 nor land insects common to both regions.' 



