160 SATURDAY LECTURES. 



Wc know that the deep sea is very cold. Cold water 

 sinks, and a submarine polar indraught of cold water must 

 replace the constant streams of tropical surface water which 

 floW' away from the equator, in order that an equilibrium 

 may be maintained. The warmest water that has been 

 found in the deep-sea (over 100 fathoms) is at 50°. 5 F. in 

 2,550 fathoms ; the ordinary temperature is but little above 

 the freezing point. This, however, d^es not affect the life 

 of organisms existing there, which are all cold blooded, 

 many of them coming into shallow water in the Arctic 

 regions. 



That many problems in regard to the deep-sea are still 

 unsolved, goes without sajang. Time does not permit me 

 to discuss them here. In conclusion, I will briefly sketch 

 the conditions of life at the bottom of the deep-sea. 



In the first place, fishes and organisms of almost every 

 marine group lower in the scale than fishes, are to be found 

 in the deeps. In order that these animals may exist where 

 the pressure of the water may be several tons to the square 

 inch, it is indispensable. that their fleshy tissues shall be so 

 loosely constituted that the water shall be able to permeate 

 them thoroughly, and thus itself equalize the external 

 pressure. Hence, the fishes and other large animals in- 

 habitating the abysses are, so far as their flesh is concerned, 

 of an almost gelatinous consistency. While they might 

 probabl}^ survive a ver}'- gradual change of pressure and be 

 able to live in shallow water, yet when they are rapidly 

 brought up from the depths in a dredge, they are invariably 

 dead, their internal organs usually turned inside out, their 

 eyes starting from their heads, and their forms more or less 

 altered from the sudden decrease of pressure and expansion 

 of the tissues. 



Other inhabitants of the sea-bed have rigid exoskeletons 

 or shells, but the soft parts are always permeable. 



While most of the deep-sea animals are small, fishes, 

 certain spider-like Crustacea and some echinoderms attain 

 a considerable size. 



As the depths must be almost entirely dark unless lighted 



