ASSIMILATIVEH COLOURATION. 395 
tage for protective purposes or as warning colours, for the single 
and sufficient reason that they are invisible.”’* Some shore species 
of crustaceans are found to turn red when kept in the dark ; 
hence Mr. Faxon is inclined to believe that in the deep-sea 
species the prevalence of red is “due to a modification of the 
pigments, induced by the darkness in which the 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.” . . . To those who may enquire 
why deep-sea crustaceans should be red-tinted in general rather 
than of any other colour, Mr. Faxon quotes Pouchet’s explana- 
tion, that ‘‘the pigments of the xanthic series (red, orange, and 
yellow) in Crustacea are contained in contractile anatomical 
elements—the chromatoblasts—while the blue pigment is never 
found in the substance of the chromatoblasts, but is held in free 
solution.” ‘‘ Under the influence of the abyssal darkness there 
is supposed to be so great an expansion of the red chromato- 
blasts that any effect from the cyanic tints is completely over- 
powered.’ t+ Another explanation has been advanced to account 
for a similar colouration of the deep-sea flora. The blue coloura- 
tion of the water is due to the decomposition or absorption of 
the red, orange, and yellow rays of light in their passage through 
the water, and owes its hue to those rays of high refrangibility, 
* © Animal Coloration,’ 2nd edit. p. 37. 
+ Review in ‘ Nat. Science,’ vol. viii. p. 119, of “* Reports on an Explora- 
tion in charge of A. Agassiz by s.s. ‘ Albatross,’ 1891, xv.: the Stalk-eyed 
Crustaceans,” by Walter Faxon. 
As regards the deep-sea fishes, according to Dr. Ginther, their colours 
‘are extremely simple, their bodies being either black or silvery; in a 
few only are some filaments or the fin-rays of a bright scarlet colour. 
Among the black forms albinos are not scarce” (‘ Introd. Study of Fishes,’ 
p. 800). On the other hand, fishes do exhibit assimilative colouration. 
Mr. Brown-Goode writes :— ‘‘ On certain ledges along the New England coast 
are rocks covered with dense growths of scarlet and crimson seaweeds. ‘The 
Codfish, the Cunner, the Sea-raven, the Rock-eel, and the Wry-mouth, which 
inhabit these brilliant groves, are all coloured to match their surroundings ; 
the Cod, which has naturally the lightest colour, being most brilliant in its 
scarlet hues, while others whose skins have a large and original supply of 
black have deeper tints of dark red and brown ”’ (‘ Science,’ vol. xv. p. 211). 
2D2 
