238 OF DEEP-SEA FISHES IN GENERAL 



a luminous ''bloom." The only specimen captured 

 glimmered like a ghost as it lay dead at the bottom 

 of a pail of turbid seawater. 



A detailed discussion of the various ways in which 

 so many fishes of the deep sea evolve light for their 

 own use would fill a small volume. 



The simplest illuminant appears to be the 

 ordinary mucus or slime secreted by the lateral line 

 of the body, and by the numerous channels that 

 traverse the bones of the head and gill-covers. Even 

 in the case of ordinary shore-fishes this slime seems 

 at times to be phosphorescent, as any one must have 

 noticed who has been out fishing at night. Bui 

 in all the true fishes of the nether ocean, such as 

 the BerycidcB, MacruridcB, and OphidiidcE, the muci- 

 ferous canals are of very singularly large size and are 

 particularly numerous. In Glyptophidium (Fig. 36), 

 which is here selected to illustrate this fact, the 

 slime-canals of the head are so capacious that the 

 bony ridges which form their boundaries stand out 

 like the frills of a ruff, when the thin skin that roofs 

 them over is removed. 



At the other end of the series we find many 

 abyssal fishes provided with highly-finished lantern-like 

 organs, consisting of — (i) a gland, which, like those 

 of the firefly, secretes a slowly-oxidising phosphorescent 

 grease ; (2) a silvery reflector, to intensify the light ; 

 and (3) a black, absorbent screen, to prevent diffusion. 



