CHARACTERISTIO 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 Scopelide, 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 air to deep-sea fishes in general. 
In his “Challenger” letters, Willämpen: Suhm speaks of the 
luminosity of Seopelus. (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 Mülleri. 4. (U. S. F. C.) 
observe the phos- 
phorescenee of the luminous spots, so arranged that it seems 
as if the anterior ones were intended to deplore the regions in 
front of the fish, while those of the belly illuminated the water 
