512 LIFE IN THE DEEP SEA. 



deep sea, crawl about protected by a Ijorrowed shell, and on 

 this, lives an animal allied to a Sea Anemone {Epizoanthiis 

 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 

 ■ purposes, and may have other uses occasionally. There is no 

 reason why a constant emission of light should be more bene- 

 ficial than a constant emission of heat, such as takes place in 

 the case of our own bodies, and it is quite conceivable that 

 animals might exist to which obscure heat-rays might be 

 visible, and to which men and Mammals generally, would 

 appear constantly luminous. 



However, whether be the light beneficial to them or not, it 

 seems certain that the deep sea must be lighted here and 

 there by greater or smaller patches of these luminous Alcyo- 

 narians, with wide intervals, probably, of total darkness inter- 

 vening ; very possibly the animals with eyes congregate round 

 these sources of light. 



The nature of the light existing in the depths, has an 

 important bearing on the question of the colouring of deep-sea 



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



