DEEP-SEA LIFE. 17 



tion Under what conditions do these inhabitants of 

 the mighty deep exist? 



Of course there are those whose lives are passed near 

 the surface, which man can readily observe; but it is 

 of the inhabitants of the great deeps that we desire 

 here to speak, and of the pressure which they must 

 sustain at such depths. 



The introduction to the Report of the Challenger 

 Expedition has some striking observations on this head, 

 as follows: 



"So far as we can judge direct sunlight does not pene- 

 trate to great depths, and consequently in deep-sea animals 

 the eyes are often absent, or are atrophied by disuse. In 

 some cases at moderate depths, where a certain amount of 

 light may still be supposed to penetrate, the eyes are large 

 and clear, exaggerated apparently, to catch its last feeble 

 rays. Many deep-sea animals are slightly and some vividly 

 phosphorescent." * 



It may be that this phosphorescence is a wonderful 

 provision of Nature, to enable these creatures to use 

 their own light to illuminate their path through these 

 regions of eternal darkness. Unfortunately " animals 

 from great depths were always brought up dead" so 

 that there was no opportunity of studying their ap- 

 pearance and movements w r hile living. Death, and the 

 great change of conditions at the surface, may have 

 greatly modified the intensity of their phosphorescence 

 while alive at great depths. There can be little doubt 

 that the cause of death was the removal of pressure. 

 That tremendous pressure, of which we can form no 

 conception, is therefore to them the prime necessity of 

 their existence. 



* Report of H.M.S. Challenger's Scientific Expedition, 1880, 

 Vol. i., p. 48 of Introduction. 



VOL. III. 2 



