482 TUBE-BLADDERED GROUP. 



tropical seas; they are so numerous that the surface-net, when used during a 

 night of moderate weather, scarcely ever fails to enclose some specimens. They 

 come to the surface at night only ; during the day, and in very rough weather, 

 they descend to depths where they are safe from sunlight or the agitation of the 

 water. Some species never rise to the surface ; indeed, scopeli have been brought 

 up in the dredge from almost any depth to two thousand five hundred fathoms." 

 Upwards of thirty species of this genus are known, and there is also an allied 

 genus (Gymnoscopelus) distinguished by the absence of scales. 



Among several other remarkable forms of the family, we may especially 

 notice a very curious fish (Ipnops) obtained at great depths during the voyage of the 



PHOSPHORESCENT SARDINE (nat. size). 



Challenger. Possessing an extremely elongate and cylindrical body, covered with 

 large, thin, deciduous scales, this fish has a depressed head and an elongate, broad, 

 spatulate muzzle, of which the whole upper surface is occupied by a luminous or 

 visual organ, divided longitudinally into two halves, and representing the highly- 

 modified eyes. The whole length of this strange fish does not exceed between 5 

 and 6 inches. Another deep-sea fish (Plagyodus) is noteworthy on account of 

 its large dimensions, and the formidable armature of its mouth ; the scaleless body 

 being long and compressed, the snout much produced, and the teeth of the jaws : 

 and palate of very unequal size, some forming long and sharply-pointed tusks. 



THE PHOSPHORESCENT SCOPELOIDS, Families STERNOPTYCHID^ 



and 



More or less nearly allied to the scopeloids are two families of deep-sea or 



pelagic fishes usually bearing phosphorescent organs along the sides of the body ; 



an example of each being represented in the accompanying illustration. 



Silvery Light- The fish (Photichthys argenteus) shown in the upper figure of the \ 



illustration, is taken as our representative of the first of the two 



families, of which, in addition to the phosphorescent organs, the leading characters 



are as follows. The body may be either covered with thin deciduous scales, or 



