THE CHARACTERS OF THE DEEP-SEA FAUNA 77 



It has been known for some years now, tliat the 

 slime secreted by the skin glands of certain sharks 

 is highly phosphorescent. It is not difficult, then, 

 to understand how it came about that certain fish 

 developed complicated phosphorescent organs. 



From the phosphorescent slime secreted by a simple 

 skin gland to the most complicated eye-like phos- 

 phorescent organ, we have a series of intermediate 

 forms that are quite sufficient, even in the imperfect 

 state of our know^ledge at the present day, to enable 

 us to understand the outlines of the evolution of these 

 peculiar and interesting organs. 



We can distinguish two kinds of phosphorescent 

 organs in the deep-sea fish. There are the curious 

 eye-like or ocellar organs situated usually in one or 

 more rows down the sides of the fish's body, forming 

 as it were a series of miniature bull's-eye lanterns to 

 illuminate the surrounding sea (fig. 6) ; and various 

 glandular organs that may be situated at the extremity 

 of the barbels or in broad patches behind the eyes or 

 in other prominent places on the head and shoulders. 



Ocellar organs have been known for many years 

 to occur on the sides of the interesting pelagic fish, 

 8copelus. Most of the species of this genus live in 

 the open sea at moderate depths, coming to the sur- 



