590 A NATURALIST ON THE " CHALLENGER. 



water representatives. Some are confined to the sea-bottom, 

 and can only crawl upon it ; others, such as the fish and shrimps, 

 have a power of extending their range vertically, but some of 

 the fish at least never rise to more than a very small height 

 above the bottom on which they live. 



Lophioid fishes, like the Angler their close ally in shallow 

 water, dangle out in the great depths their lures from above their 

 huge mouths, to attract their prey. Hermit-crabs in the deep 

 sea, crawl about protected by a borrowed shell, and on this, lives 

 an animal allied to a Sea Anemone (Epizoantlms parasiticus), so 

 that the combination is closely similar to that so familiar in 

 shallow seas. Pycnogonid larvse rear themselves as parasites 

 within Hydroid colonies in the depths, just as in the shallows. 



The depths of the sea being mostly dark, many of the 

 animals inhabiting them are blind, like cave animals, and have 

 their eyes reduced to mere rudiments. Many of these, such as 

 some blind fish and Crustacea, are provided with enormously 

 long and delicate feelers or hairs, in order that they may feel 

 their way about with these, just as a blind man does with the 

 aid of his stick. 



Other deep-sea animals have their eyes enormously enlarged, 

 and thus make the best of the little light there is in the depths. 

 This light is, no doubt, as suggested in the early days of deep- 

 sea dredging by Dr. Carpenter, Sir Wyville Thomson, and Mr. 

 Gwyn Jeffreys,* that emitted by phosphorescent animals, 

 especially Alcyonarians. 



All the Alcyonarians dredged by the " Challenger " in deep 

 water, were found to be brilliantly phosphorescent when brought 

 to the surface, and their phosphorescence was found to agree in 

 its manner of exhibition with that observed in the case of 

 shallow-water forms. There seems no reason why these animals 

 should not emit light when living in deep water, just as do their 

 shallow- water relatives. 



The light emitted by phosphorescent animals is quite pos- 

 sibly in some instances to be regarded only as an accidental 

 product, and of no use to the animal producing it, although of 

 course, in some cases, it has been turned to account for sexual 



* " Proc. Roy. Soc, 1869," p. 431. 



