I82 



SCIENTIFIC NEWS. 



[Feb. 24, 1888. 



undergoes the necessary change of freedom from enor- 

 mous pressure. It is a much more extreme form of the 

 result of light air in high balloon altitudes. In every 

 living organism with an intestinal tract there are accumu- 

 lations of free gases. Under greatly diminished pressure 

 these gases expand ; so that if the change from low 

 depths to much higher strata be sudden, the various 

 tissues must be distended and ruptured. What is a 

 vigorous fish at a depth of 3,000 feet (with a pressure 

 of half a ton on every square inch of its surface) 

 appears at the surface as a loosely-jointed body. When, 

 during the struggle which occasionally takes place 

 between the fish and its prey, the fish is carried out of 

 its regular depth into a somewhat higher stratum, the 

 expansion of the gases will cause both to ascend towards 

 the surface, especially if the prey-fish has an air-bladder, 

 and the rate of speed will increase as the pressure is 

 dirriinished ; so that a rupture takes place in its thin 

 skin and death ensues. One point Dr. Giinther made out 

 clearly, that abyssal life has exercised no influence on the 

 development of an air-bladder; in none did he find an open 

 communication between the air-bladder and the gullet. 



The branches of the muciferous system are dilated to 

 an extraordinary degree. All the cavities and canals are 

 filled with an immense quantity of mucus, which swells 

 by immersion in water ; but its physiological use is not 

 yet known. Dr. Gunther suggests that it is to surround 

 the fish with luminositj-, the more so as the mucus has 

 been actually observed to have phosphorescent properties 

 in newly-caught specimens. 



The so-called phosphorescent organs have been noticed 

 ever since the first species was described ; but they were 

 regarded as peculiar piquant spots or modified portions 

 of the scales. Cocco (1838) first asserted that the pair 

 ot whitish gland-like bodies on the upper side of the 

 snout have phosphorescent properties ; but Ussow (1879) 

 declares them to be accessory eyes. Leydig (1881) 

 holds the opinion that they are " pseudo-electric " organs, 

 which emit light ; but Emery (1884) adopts the view of 

 their phosphorescent nature. 



During Dr. Gilnther's examination of the Challenger 

 fishes he found the luminous organs widely distributed 

 over the various organs of the body, but not equally so 

 among the various families. When, however, the 

 muciferous system is most developed, the luminous 

 organs are almost entirely absent — that is a remarkable 

 fact. These organs present many modifications as 

 regards their seat, appearance and structure. In their 

 most primitive condition they appear as innumerable 

 minute tubercles more or less raised above the surface of 

 the skin, and covering the sides of the body ; they are 

 crowded together in transverse bands, corresponding to 

 the segments of the muscular system. More differentiated 

 are the eye-like spots, of a white colour in preserved 

 specimens, and red or green during life in several 

 specimens. In others, still more differentiated, are large 

 round flat organs of a peculiar mother-of-pearl brightness, 

 arranged in rows on the lower side of the bodv and head. 



Light-producing organs are very generally distributed 

 in the deep-sea fishes, and those parts of the depths of 

 the sea in which phosphorescent animals are abundant 

 must be sufficiently illuminated to enable such of them 

 as are provided with well-developed eyes to perceive 

 objects with as much distinctness as do the forms which 

 sport at the surface at night, and are dependent on the 

 fight of the moon and stars and the general phosphore- 

 scent light around them. There is no doubt that fishes 



contribute a considerable amount of this luminosity of the 

 abyssal depths. 



This fight may be produced by the luminous organ to 

 enable its possessor to see. It proceeds from the gene- 

 ral surface when the fish is active, and ceases when it is 

 at rest. In those fishes in which the organs are very 

 highly developed, the production of light seems to be 

 subject to the will of the animals. If the light were 

 constant, or if it were not under the control of the fish, 

 then it would be a beacon to scare its prey, rather than 

 a help to secure it. The attacking fish seems to be 

 able to shoot rays of light in the direction which it wishes- 

 to explore for the purpose of discovering or following up- 

 its prey. Dr. Gunther compares them to a constable's 

 " bull's-eye " lantern, which can be opened or shut at 

 his will. 



The luminous organs which are placed on fin-rays or 

 tentacles are for attracting smaller fishes. It is well- 

 known (as in salmon spearing) that aquatic animals are 

 in the dark attracted by a light ; and therefore these 

 luminous appendages prove most efficient lures in the 

 abyssal darkness, to attract prey for the rapacious assail- 

 ant. The comparatively rare occurrence of special 

 organs of touch in deep-sea fishes, show that the majo- 

 rity depend on the sense of sight for the perception of 

 surrounding objects, and that therefore a large amount 

 of light must be distributed, at least locally, in depths to 

 which the surface light does not penetrate. 



The gill-laminse appear short and shrunken, and re- 

 duced in number ; nor do they possess the same extent 

 of respiratory surface, so that the intensity of the breath- 

 ing process seems to be more diminished than in surface 

 fishes. Doubtless dwelling at such a depth must have 

 some effect upon circulation, respiration, assimilation ot 

 food and secretion ; but Dr. Gunther does not hazard a 

 conjecture as to the manner and degree in which these 

 functions may differ from those of surface fishes. 



It is curious to notice that the spawn of some deep- 

 sea fishes is developed at the surface, whilst mature in- 

 dividuals reside at more or less considerable depths. 

 Dr. Gunther does not think that these fishes rise to the 

 surface at the season of propagation ; but he is of 

 opinion that the spawn is deposited at a depth of several 

 thousand feet, and gradually rises to the surface. The 

 young fry, after a short sportive life near the surface, 

 with patriotic sympathies return to the depths of their 

 progenitors. In the case of others, the spawn remains 

 at the bottom of the sea throughout the period of its 

 development. But there is a marked difference between 

 the two kinds of fishes ; the one developed under the- 

 accelerating influences of light, warmth, and oxygen, 

 supplies the deep sea with the forms which retain the 

 organisation of the surface fishes ; the other slowly 

 developed under the retarding conditions of darkness,, 

 cold, and deficient oxygen, supplies those degraded forms 

 which otherwise cannot be accounted for. 



Dr. Gunther reports that the colours of deep-sea 

 fishes are extremely simple, their bodies being either 

 black, pink, or silvery ; some are of a bluish colour ; in 

 a few are some fin-rays of a bright scarlet hue ; but black 

 spots on the fins or dark cross-bars on the body are ol 

 very rare occurrence. The body-cavities are generally 

 coloured black. The highly specialised luminous organs, 

 on the head of some species are green or pink during 

 life, whilst they fade into white after the immersion ot 

 the fishes in preserving spirit. Among the black-coloured 

 deep-sea fishes, albinos are not scarce. 



