CLASS PISCES 



473 



temperature is always a few degrees above the freezing-point; 

 the pressure is a ton or more to the square inch, whereas it is 

 only about fifteen pounds at the surface; and there is no vege- 

 tation, so that the inhabitants of the depths must be carnivorous 

 or live on organisms that sink toward the bottom. 



Fishes meet these conditions in various ways and are often 

 curiously modified. Some have very large eyes so as to catch 



Fig. 408. — A deep-sea fish, Stomias boa. The white dots are the luminous 

 organs. (From Parker and Haswell, after Filhol.) 



as many rays of light as possible; these eyes probably serve in 

 connection with phosphorescent organs. Others have small or 

 rudimentary eyes and are blind; they depend upon tactile organs 

 instead of eyes. Many have large mouths with long, sharp teeth, 

 and enormous stomachs. The phosphorescent organs are vari- 

 ously distributed over the body (small circular areas in Fig. 

 40S). Some of them consist of a cup of secretory cells covered 

 by a cellular lens. The secretion is luminous, and in certain cases 

 acts as a lure; in others it probably enables the fish to see in 

 the dark abyss of the ocean. 



