REPORT ON THE DEEP-SEA FISHES. XXxi 



I am also of opinion that the highly specialised organs which are placed on the dorsal 

 and ventral sides of the caudal peduncle of many Scopelids and Sternoptychids, have the 

 function of attracting prey, and not of enabling their possessors to see. Situated at the 

 posterior extremity of the body, they would be in a most unfavourable position to throw 

 the light wdthin the area of vision by the eye. On the other hand, when we recollect the 

 peculiar motion of a Scopelus, which darts rapidly in short curves to' the right and left, 

 upwards and downwards, we can understand that these posterior organs are of great 

 assistance to the fish in picking up any creatures which, attracted liy the gleam 

 of light issuing from its tail, are lured into too near a proximity. The explanation that 

 these caudal organs shoot out rays of hght to frighten aw-ay a pursuer, does not seem to 

 me a happy idea. They are, as I assume, subject to the will of the fish, which when 

 pursued would simply extinguish its lantern and escape into darkness ; light w^ould not 

 frighten, but rather attract a pursuer. 



Special organs of touch are not more generally developed in deep-sea fishes than in 

 the littoral fauna. As such may be considered the ventral filaments of the Ophidiidae, 

 the more or less detached rays of the pectoral fin of Pteroidonus, Microlene and Mixonus, 

 and especially of Bathypterois which possesses but rudimentary eyes, and the pectoral 

 filaments of which remind one of those of the Polynemidae. Indeed, the comparatively 

 rare occurrence of special organs of touch in deep-sea fishes may be used as evidence that 

 the majority depend on the sense of sight for the perception of surrounding objects, and 

 that therefore a la.rge amount of light must be distributed, at least locally, in depths to 

 which the surface light does not penetrate. 



The excessively elongate fin-rays of young Trachypteridje are evidently not organs of 

 touch ; it is difficult to explain their use in those young fishes ; it might he imagined 

 that they would ])e rather disadvantageous to them by attracting other fishes of 

 prey, unless they afford protection by then- resemblance to delicate fronds of fucus 

 floating in the water or gradually settling towards the bottom. Such delicate filaments 

 can only be developed in fishes sojourning in water which is not subject to violent 



asjitation. 



In the subsequent descriptions of deep-sea fishes frequent mention is made of the 

 reduction in size and length of the gill-laminae. These organs appear short and shrunken ; 

 it is possible that they are longer during life, ending in delicate points, and shrunken only 

 in consequence of the action of the spirit, but the horny rods which support the plaits of 

 the mucous membrane are also wanting in firmness, like the parts of the skeleton, and are 

 much shorter than in the ordinary Teleostean type. The lamiuas are also reduced in 

 number, and the gill does not possess the same extent of respiratory surface, so that 

 the intensity of ttie respiratory process seems to be more diminished than in surface 

 fishes. We can hardly doubt that the sojourn in the low temperature of the abyssal 

 depths must have some efiect upon circulation, respiration, assimilation of food 



