CHARACTERISTIC DEEP-SEA TYPES. FISHES. 33 



it may be extended in front of the head and used as an organ of 

 exploration, so that we may imagine this fish feeling its way in 

 the dark, and exploring the ooze to discover buried in it the 

 animal upon which it feeds. 



To the " pelagic Isospondyli " belong those groups which, like 

 the Scopelidse, are found from time to time at the surface, liv- 

 ing or dead, and which, there is reason to believe, inhabit the 

 intermediate depths of the ocean, having the power of ascend- 

 ing and descending developed to an extent which is not at 

 present understood. 



Among the deep-water groups named above occur the most 

 abnormal specializations, such as powerful jaws, lancet-like teeth, 

 prolonged tactile appendages, and enlargement of the tube-bear- 

 ing scales. They have not the cavernous and feeble skeletons 

 peculiar to the deep-sea gadoids, and many other families, which 

 may have found their way gradually into deep water ; they are, 

 as a rule, compactly built, muscular, and are the most actively 

 predaceous of the abyssal forms. 



The pelagic groups do not, as a rule, exhibit special modifica- 

 tions of form, but they are, with few exceptions, provided with 

 peculiar luminous appendages, which, like the cavernous skele- 

 tons and exaggerated mucous systems, have been by many wri- 

 ters attributed to deep-sea fishes in general. 



In his " Challenger " letters, Willemoes-Suhm speaks of the 

 luminosity of Scopelus. (Fig. 219.) It is well known to the 

 fishermen of the 

 Mediterranean 

 that at the death 

 of the fish the 

 luminosity ceases. 

 We frequently 

 brought in scope- 

 lids in our tow- 



nets, and could Fig. 219. Scopelus Muiieri. f (U. s. F. c.) 



observe the phos- 

 phorescence of the luminous spots, so arranged that it seems 

 as if the anterior ones were intended to explore the regions in 

 front of the fish, while those of the belly illuminated the water 



