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 c@lolepis, 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 2,485 
fathoms Scrobicularia nitida, MULLER, 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 
D 
