THEIR COLOURS 233 



possess, the elaborate mucous-canal-system of deep- 

 sea fishes is part of a specially - delicate tactile 

 mechanism. 



The absence or deficiency of sunlight, which makes 

 colour-markings of no moment, is very reasonably 

 supposed to explain the facts that the majority of 

 deep-sea fishes are of a uniform — and usually sombre 

 — colour, and that only a minority are banded, 

 striped, or otherwise marked in definite patterns ; but 

 this again is a subject that is open to much discus- 

 sion, by reason of our inability rigidly to define its 

 compass. Our observations in the Investigator extend 

 to 1 68 species which have been dredged below the 

 loo-fathom line : of these, fifty-two were black, or some 

 shade of blue, or purple-black ; fifty-six were some 

 shade of dull brown, ten were silvered over a blackish 

 or brownish ground colour, ten were bright silver, and 

 four were grey; making a total of 132 — or 78 per 

 cent. — simply-coloured species. Again, fourteen species, 

 mostly among those living between 100 and 250 

 fathoms, were of a nearly uniform red or rosy hue, 

 this very possibly being the colour of the daylight — 

 like the sun's disk in a fog — at those depths. On 

 the other hand, only eighteen species, and these for 

 the most part species found near the loo-fathom line, 

 were striped, or marked with recognisable patterns, 

 and only four species were brilliantly variegated with 

 many colours. 



