4^4 



TUBE-BLADDERED GROUP. 



Monsieur Filhol 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, tilling 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 (j^ nat. 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 

 e}^e, 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 

 Stomias, 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 



