4 3 4 TUBE-BLADDERED GROUP. 
Monsieur Filliol writes that “ the existence of eyes in fishes which we believe to 
live in a dark medium, seems at first sight impossible to understand. But this fact 
receives an explanation when we learn that the creatures furnished with these 
organs are covered with a coating of luminous mucus, or bear phosphorescent 
plates. The phosphorescence with which the fishes of the ocean depths are endowed 
serves indeed both to guide them and to attract their prey, filling for them in the 
latter case the same office as a torch in the hand of a fisherman. This peculiarity 
has been long noticed in surface-fishes which pursue their prey at night; Bennett, 
for instance, having described a shark which gives off a bright green phosphor¬ 
escence from the lower surface of its body. On one occasion that zoologist 
brought into a room a freshly-caught specimen of this shark, upon which the 
whole chamber was illuminated with the light given off from its body. It is 
probable that the different species of sharks living at moderate depths, like the one 
the dorab (w u a t. size). 
described by Bennett, make use of their luminosity solely for the purpose of 
attracting their prey within reach. In most cases the origin of this light-giving 
mucus must be attributed to glandular organs distributed along the flanks and tail, 
on the head, and more rarely on the back. There exists, however, in certain fishes, 
which lack these glandular organs, an apparatus of a totally different nature for 
the emission of light; this apparatus consisting of a kind of biconvex transparent 
lens closing the front of a chamber filled with clear fluid. This cavity is carpeted 
by a blackish membrane, formed of hexagonal cells, thus recalling the retina of the 
eye, and is connected with certain nerves. Phosphorescent plates of this type 
may be situated either beneath the eyes, or on the sides of the body,” one of the 
fishes thus furnished belonging to the family now under consideration, in which it 
forms the genus Malacosteus. A specimen of this fish captured before death had 
ensued was observed to emit a yellowish light from the uppermost plate beneath 
the eye, while that from the lower plate had a greenish tinge. In the genus 
titomias, continues our author, “ the sides of the body present a double longitudinal 
series of phosphorescent plates, which emit light in such a manner as to cause the 
