464 THE POPULAR SCIENCE MONTHLY. 



hundred fathoms. Moseley says that " probably all is dark below 

 two hundred fathoms excepting in so far as light is given out by 

 phosphorescent animals/' and Wyville Thomson speaks of the 

 " utter darkness of the deep-sea bottom." 



"Within the last few years a few authors have maintained that 

 it is quite possible that a few rays of sunlight do penetrate even 

 to the greatest depths of the ocean a view mainly based on the 

 fact that so many deep-sea animals possess extremely perfect and 

 complicated eyes and very brilliant colors. Verrill says : " It 

 seems to me probable that more or less sunlight does actually 

 penetrate to the greatest depths of the ocean^ in the form of a soft 

 sea-green light, perhaps at two or three thousand fathoms equal 

 in intensity to our partially moonlight nights, and possibly at the 

 greatest depths equal only to starlight. It must be remembered 

 that in the deep sea far away from land the water is far more 

 transparent than near the coast." Packard is of a similar opinion. 



There seem to me to be very slight grounds for this view. 

 The fact that, comparatively speaking, shallow-water fish avoid 

 nets that are rendered phosphorescent by entangled jellyfish does 

 not justify us in assuming that deep-sea fish avoid regions where 

 there are phosphorescent Gorgonians or Pennatulids. It is not 

 by any means certain that fish avoid sunken nets on account of 

 their phosphorescence. Most fish possess, as is well known, a very 

 acute sense of smell, and it is very probable that they avoid such 

 nets on account of the putrid odors of the dead animals that re- 

 main attached to them. 



Nor is there much strength in the further argument that it 

 can hardly be possible that there can be an amount of phospho- 

 rescent light regularly evolved by the few deep-sea animals, having 

 this power, sufiicient to cause any general illumination, or power- 

 ful enough to have influenced, over the whole ocean, the evolution 

 of complex eyes, brilliant and complex protective colors, and com- 

 plex commensal adaptations. 



We have no sound information to go upon to be able to judge 

 of the amount of light given off by phosphorescent animals at the 

 bottom of the deep sea. The faint light they show on deck after 

 their long journey from the depths in which they live to the sur- 

 face may be extremely small compared with the light they give 

 in their natural home under a pressure of two tons and a half to 

 the square inch. The complex eyes that many deep-sea animals 

 exhibit were almost certainly not evolved as such, but are simple 

 modifications of eyes possessed by a shallow-water ancestry. 



The more recent experiments that have been made tend to show 

 that no sunlight whatever penetrates to a greater depth, to take 

 an extreme limit, than five hundred fathoms. Fol and Sarasin, 

 experimenting with very sensitive bromo-gelatin plates, found 



