Chap, xxii.] COLOURS OF DEEP-SEA ANIMALS. 



51, 



animals. I examined the phosphorescent Hght emitted by' 

 three species of deep-sea Alcyonarians with the spectroscope, 

 and found it to consist of red, yellow, and green rays only.' 

 Hence, were the light in the deep sea derived from this source 

 alone, in the absence of blue and violet light, only red, yellow, 

 and green colours in animals could be effective ; no blue 

 animals were obtained in deep water, but blue animals are not 

 common elsewhere. 



It is remarkable that almost all the deep-sea shrimps and 

 Schizopods, which were obtained in very great abundance, are 

 of an intense bright scarlet colour, differing markedly in their 

 intensity of colouring from shallow-water forms, and having, 

 apparently for some purpose, developed an unusually large 

 quantity of the same red pigment matter which colours small 

 surface Crustacea. 



Dr. Wallich refers at length in his work, cited above,* to the 

 absence of light in the deep sea, and explains the possibility of 

 persistence of colouring in deep-sea animals, even though diey 

 live in absolute darkness. Many deep-sea Holothurians are 

 coloured of a deep purple ; no doubt the colouring is useless 

 in their case, and is merely due to the persistence of a colour- 

 ing developed originally in shallow-water ancestors. 



The same purple colouring matter, which is easily distin- 

 guished by means of the spectroscope, occurs in a shallow- 

 water (nine fathoms) Coniatitla at Cape York, in the tropics, 

 and in a Holothurian, found in 1,955 fathoms, near the 

 Antarctic Sea. Many deep-sea Corals have their soft structures 

 tinged with a madder colouring matter which occurs also in 

 surface-swimming Medusae of various kinds.t 



No doubt, in the case of many deep-sea possessors of com- 

 plex colouring matters, these pigments never exercise their 

 peculiar action on light during the whole life of the animals, 

 but remain in darkness, never showing their colour at all. 

 Similarly in the case of many Mammalia, with thick or fur-clad 

 skins, the bright red colouring matter of the blood never sees 

 the light or appears as a red colour. It is only in a few 

 Mammals that this red colouring matter is turned to account, 

 as, for example, in the white races of man, in which case 

 sexual selection has brought about a tinging of the cheeks 

 by its aid. 



Most deep-sea fish are of a dull black colour, some are 



* " The Atlantic Sea Bed," p. 108. 



t For observations on the Colouring of Deep-Sea Animals, see H. N. 

 Moseley, "On the Colouring Matters of Various Animals. tspeciall\' of 

 Deep-Sea Forms dredged by H.M.S. 'Challenger." Quart. Journ. 

 Micro. Sci., Vol. XVII., New Sen, p. I. 



