PHYSICAL CONDITIONS OF THE DEEP SEA. 465 



that there was no reaction after ten minutes' exposure at a depth 

 of four hundred metres on a sunny day in March. But although 

 it is very highly probable that not a glimmer of sunlight ever 

 penetrates to the depths of the ocean, there is in some places, un- 

 doubtedly, a very considerable illumination due to the phospho- 

 rescence of the inhabitants of the deep waters. 



All the Alcyonarians are, according to Moseley, brilliantly 

 phosphorescent when brought to the surface. Many deep-sea fish 

 possess phosphorescent organs, and it is quite possible that many 

 of the deep-sea protozoa, tunicates, jellyfish, and Crustacea are 

 in their native haunts capable of giving out a very considerable 

 amount of phosphorescent light. If we may be allowed to com- 

 pare the light of abysmal animals with that of surface forms, we 

 can readily imagine that some regions of the sea may be as 

 brightly illuminated as a European street is at night an illumi- 

 nation with many very bright centers and many dark shadows, 

 but quite sufficient for a vertebrate eye to distinguish readily and 

 at a considerable distance both form and color. 



To give an example of the extent to which the illumination 

 due to phosphorescent organisms may reach, I may quote a 

 passage from the writings of the late Sir Wy ville Thomson : 

 " After leaving the Cape Verd Islands the sea was a perfect 

 blaze of phosphorescence. There was no moon, and although the 

 night was perfectly clear and the stars shone brightly, the luster 

 of the heavens was fairly eclipsed by that of the sea. It was easy 

 to read the smallest print, sitting at the after-port in my cabin, 

 and the bows shed on either side rapidly widening wedges of ra- 

 diance so vivid as to throw the sails and rigging into distinct 

 lights and shadows." 



A very similar sight may frequently be seen in the Banda seas, 

 where on calm nights the whole surface of the ocean seems to be 

 a sheet of milky fire. The light is not only to be seen where the 

 crests of waves are breaking, or the surface disturbed by the bows 

 of the boat, but the phosphorescence extends as far as the eye can 

 reach in all directions. It is impossible, of course, to say with any 

 degree of certainty whether phosphorescence such as this exists at 

 the bottom of the deep sea, but it is quite probable that it does in 

 some places, and hence the well-developed eyes and brilliant 

 colors of some of the deep-sea animals. On the other hand, the 

 entire absence or rudimentary condition of the eyes of a very con- 

 siderable proportion of deep-sea animals seems to prove that the 

 phosphorescent illumination is not universally distributed, and 

 that there must be some regions in which the darkness is so abso- 

 lute that it can only be compared with the darkness of the great 

 caves. 



It may be stated then with some confidence that in the abysmal 



VOL. XL1V. 36 



