230 OF DEEP-SEA FISHES IN GENERAL 



their prime, and on the other hand a suggestive 

 absence or paucity of some of the more modern marine 

 groups, such as the Lophobranchii and Plectognathi ; 

 so that it may fairly be said of the fish-fauna of the 

 depths that, as a whole, it has a slightly more anti- 

 quated make-up than that of the littoral,"^ and we shall 

 notice hereafter that the same thing holds good of the 

 the stalk-eyed Crustacea, and perhaps of some other 

 groups also. 



We have already referred to the peculiar conditions 

 of life in the depths of the sea ; they are such as are 

 determined by greatly increased pressure, by absence 

 of sunlight and consequent absence of all vegetation 

 except bacteria, by permanent low temperature, and 

 perhaps by diminished supplies of oxygen. 



One of the effects of the enormous increase of 



pressure is that bones and muscles which at the 



ordinary pressure of the atmosphere (14.7 lbs. to the 



square inch) are so fragile as hardly to hang together, 



are perfectly solid and coherent, this being the inverse 



statement of the fact that when a deep-sea fish, which 



presumably led an active life, is brought to the surface, 



how gradually and carefully soever, its bones are often 



like so much touchwood, and its muscles like so much 



rotten pulp, while its eyes are burst from their sockets, 



* This proposition expressly refers only to marine fishes, not to 

 freshwater fishes, among which a few " living fossils " still survive, 

 giving the freshwater fauna a more archaic connection than any part 

 of the marine fauna, as far as fishes are concerned. 



