GENERAL DISCUSSION. 15 



ing brown spots, tlie whole fading rapidly in alcohol ; the allied species, M. 

 spinulosa, from 511 fathoms, Plate XXI., has retained the spots, marks of an- 

 cestry and of recent differentiation, but has become blacker and has lost the 

 yellow and the white vermiculations ; and M. spimsa, PI. XXII., from 

 depths of 1020 to 1270 fathoms lacks all spots and is unifcu'in blackish. 

 The pale greenish to yellowish or to bluish assimilative tint, seen on most of 

 the colored plates herewith, is decidedly fugitive and disappears soon after 

 death of the specimen, or after application of the preserving liquids; in 

 many if not most in.stauces it appears to be little more than the luminosity 

 affecting the great majority of abyssal creatures. For instances see the 

 sharks Isistius, Centroscyllium, and Chlamydoselachus, or the fishes 

 Caulolepis, Dicrolene, Macrurus, and others. The occultative luminosity is 

 genei'ally distributed over the body and is to be distinguished from the 

 monstrative light seen in the lanterns, flashlights, reflectors, lures, etc., of 

 particular genera. The latter is a light pertaining to specialized organs of 

 various species, is of a variety of tints, and serves on some fishes as means 

 of recognition by kindred and on others to decoy and bring the prey within 

 reach. The Scopeloids furnish good examples of the recognition marks 

 (siffiia), and in the Pedicnlates instances are to be seen of a great variety of 

 the lures {lUicia). As is necessary' for its discovery in the light in which it 

 is nsed, the monstrative light is much the stronger ; it varies in colors ac- 

 cording to the genus or the species on which it is developed ; and when in 

 function is more or less completely under the control of the individual in 

 respect to appearance, disappearance and brilliancy. The structure of the 

 different monstrative organs on a number of the species has been well 

 worked out by Lendenfeld in Giinther's report on the deep sea fishes of 

 the "Challenger Expedition." Creatures living in the ooze in many cases 

 are of an intense black in which no luminosity can positively be asserted 

 to exist ; on such of these as are possessed of lures the latter are most 

 often directed upward as if to capture a prey swimming above them, 

 for instance Dolopichthys of Plate XIII. Many of the Stomiatoids and 

 the Mur^noids al.'^o are of the same deep black ; it would appear as if 

 the former inhabited the lower edge of the dark or azoic zone, their lures 

 are extended downward as if to secure prey approaching from below. 



The condition of the eyes of deep sea fishes is itnportant evidence in sup- 

 port of the theory of an abysmal light ; it also tends to establi.sh the idea 

 that this light in comparison with that of the sun is very weak indeed. 



