34 THREE CRUISES OF THE “BLAKE.” 
beneath 1t. 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 resplen- 
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.! 
Malacosteus is the sole representative of a peculiar family, the 
affinities of which have never been defined. Malacosteus niger 
In fishes 
1 The existence of well-developed eyes 
among fishes destined to live in the dark 
abysses of the ocean seems at first con- 
tradietory ; but we must remember that 
these denizens of the deep are immigrants 
from the shore and from the surface. In 
some cases the eyes have not been spe- 
cially modified, but in others there have 
been modifications of a luminous mucous 
membrane, leading on the one hand to 
phosphorescent organs more or less spe- 
cialized, or on the other to such remark- 
able structures as the eyes of Ipnops, 
intermediate between true eyes and spe- 
cialized phosphorescent plates. 
that have been blinded and retain for 
their guidance only the general sensibility 
of the integuments and of the lateral line, 
these parts soon acquire a very great de- 
licacy. The same is the case with tactile 
organs, and experiments show that bar- 
bels may become organs of touch adapted 
to aquatie life, sensitive to the faintest 
movements or the slightest displacement, 
with power to give the blinded fishes full 
cognizance of the state of the medium in 
which they live. 
