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COLORS OF THE DEEP-SEA CRUSTACEA. 



253 



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f 



ness in which these creatures dwell^ either through chemical action or more 

 probably through a physiological process originating in the eye and affecting 

 the pigment cells by a reflex action. In either case the prime cause is a 

 purely physical one^ — the more or less complete absence of light in the 

 depths of the sea. This color, then, is to be regarded as entirely useless to 



its possessor. 

 ' The retention of pigment and functional eyes through a long succession 



of o-encrations among the deep-sea Crustacea implies the existence of a cer- 

 tain amount of light at depths for beyond the point where it can be demon- 

 strated by experiments with photographic plates.* Although many of 

 thesp animals are blind and show a strong tendency to become colorless, yet 

 many are endowed wdth very highly developed eyes and display pronounced 

 colors formiuf>- a strong contrast in both respects to the fauna of subter- 

 ranean caverns. The free-swimming Crustacea from great depths are, as ^ve 

 have seen commonly of a very bright red color and endowed with visual 

 origins of a hif>'h order, while the bottom sj^ecies, even those from much shal- 

 lower depths, are most often pale of hue and frequently blind. This difference 

 is to be explained through the different mode of life followed by the two 

 classes. Powerful and active swimmers, such as the Notostomi and Gnatho- 

 phausio) are fitted by their mode of life, to take advantage of what little 

 hVht exists at those depths, whether it be some feeble rays which penetrate 

 from above or the pale phosphoric gleams evoked by their passage through 

 the deep. The more sedentary, bottom species, on the other hand, would be 

 prone to conceal themselves in the mud or whatever retreat the sea-floor 

 mio'ht afford. Hence the aptness of these forms to lose both their pigments 



and their sense of sight. 



Colors of the cyanic series, — blues and greens, — although not uncom- 



mon amon<^ surface and shore Crustacea, are almost never seen in the species 

 from the deeper waters. It is remarkable, however, that the eggs of many 

 of the red deep-water Crustacea sliow during the period of incubation bright 

 blue or sometimes green tints. Mr. Agassizf lias noted this, and the late Pro- 

 fessor J. Wood-Mason specified many such cases, in his accoimt of the Crus- 

 tacea dredo-ed by the steamer " Investigator." It seems likely, therefore, 

 that the blue pigments arc not really lacking in the adult, but merely over- 



* Cf Ful and Sarasiii, Coniptcs llciidus, XCIX. 793, C 100, and Clmii, Die pelagische Tliierwclt, etc., 

 p 59 (Biblioilicca Zoologlca, Ersicr Band, Heft 1, 188S). 

 t Bull. Mas. Oomp. Zoul, XXIII. 89, 1892. 



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