34 THREE CRUISES OF THE " BLAKE." 



beneath it. The "Bombay duck," so common at certain peri- 

 ods in the Indian Ocean, belongs to this group of phosphores- 

 cent fishes. It is probably, with Scopelus, an inhabitant of 

 deep water, coming to the surface only at certain times. 



We may imagine some deep-sea types, when in search of their 

 food, illuminating the water around them to a certain extent by 

 their feeble phosphorescent light. Others carry beacons or spe- 

 cialized plates on certain parts of the head ; others are resjnen- 

 dent with phosphorescent spots extending along the sides of the 

 body, or the back, or ventral surface ; while in others, again, 

 long tactile appendages play the part of lights sent out to illu- 

 minate dark corners, or the fins themselves may be intensely 

 luminous. Sometimes the whole body is phosphorescent, and 

 diffuses a subdued light, as is the case with some of the deep- 

 sea sharks. It is hoped that future investigations will solve for 

 us the question whether all these phosphorescent fishes are not 

 to a greater or less extent in the habit of swimming far from 

 the bottom. 



Ipnops is evidently a dweller on the bottom. The eyes of this 

 fish have been carefully examined by Professor Moseley. They 

 were at first considered phosphorescent organs, but they show a 

 flattened cornea extending along the median line of the snout, 

 with a large retina composed of peculiar rods, which form a 

 complicated apparatus, destined undoubtedly to produce an 

 image and to receive especial luminous rays. 1 



Malacosteus is the sole representative of a peculiar family, the 

 affinities of which have never been defined. Malacosteus niger 



1 The existence of well-developed eves cialized phosphorescent plates. In fishes 



among fishes destined to live in the dark that have heen blinded and retain for 



abysses of the ocean seems at first con- their guidance only the general sensibility 



tradictory ; but we must remember that of the integuments and of the lateral line, 



these denizens of the deep are immigrants these parts soon acquire a very great de- 



from the shore and from the surface. In licacy. The same is the ease with tactile 



some cases the eyes have not been spe- organs, and experiments show that bar- 



cially modified, but in others there have bels may become organs of touch adapted 



been modifications of a luminous mucous to aquatic life, sensitive to the faintest 



membrane, leading on the one hand to movements or the slightest displacement, 



phosphorescent organs more or less spe- with power to give the blinded fishes full 



cialized, or on the other to such remark- cognizance of the state of the medium in 



able structures as the eyes of Ipnops, which they live. 

 intermediate between true eyes and spe- 



