chap, i.] INTRODUCTION. 33 



tion to move our bodies in the denser medium. We are 

 already familiar, chiefly through the researches of the 

 late Professor Sars, with a long list of animals of all 

 the invertebrate groups living at a depth of 300 to 

 400 fathoms, and consequently subject to a pressure 

 of 1,120 lbs. on the square inch ; and off the coast of 

 Portugal there is a great fishery of sharks (Centros- 

 cymnus coelolepis, Boc. and Cap.), carried on beyond 

 that depth. 



If an animal so high in the scale of organization 

 as a shark can bear without inconvenience the 

 pressure of half a ton on the square inch, it is a 

 sufficient proof that the pressure is applied under 

 circumstances which prevent its affecting it to its 

 prejudice, and there seems to be no reason why 

 it should not tolerate equally well a pressure of 

 one or two tons. At all events it is a fact that 

 the animals of all the invertebrate classes which 

 abound at a depth of 2,000 fathoms do bear that 

 extreme pressure, and that they do not seem to be 

 affected by it in any way. "We dredged at 2,435 

 fathoms Scrohicularia nitida, JVIuller, a species 

 which is abundant in six fathoms and at all inter- 

 mediate depths, and at 2,090 fathoms a large Fusus, 

 with species of many genera which are familiar at 

 moderate depths. Although highly organized animals 

 may live when permanently subjected to these high 

 pressures, it is by no means certain that they could 

 survive the change of condition involved in the pres- 

 sure being suddenly removed. Most of the mollusca 

 and annelids brought up in the dredge from beyond 

 1,000 fathoms were either dead or in a very sluggish 

 state. Some of the star-fishes moved for some time 



v 



