GKOGRAPHICAL DISTRIBUTION OF ANIMALS 305 
The bassalian fauna, or deep-sea fauna, is composed of 
species inhabiting great depths (2,500 feet to 25,000 feet) 
in the sea. At a short distance below the surface the 
change in temperature from day to night is no ionger felt. 
At a still lower depth there is no difference between winter 
and summer, and still lower none between day and night. 
The bassalian fishes in- 
habit a region of great 
cold and inky darkness. 
Their bodies are subjected 
to great pressure, and the 
conditions of life are prac- 
tically unvarying. There 
is therefore among them 
no migration, no seasonal 
change, no spawning sea- 
son fixed by outside con- 
ditions, and no need of 
adaptation to varying en- 
vironment. Asa result, all 
are uniform indigo-black 
in color, and all show more 
or less degeneration in 
those characters associated 
with ordinary environ- 
ment. Their bodies are : 
elongate, from the lack of — Fre. 180—A crinoia (Rhizocrinus woroten 
specialization in the ver- fi, A duper anima whch tres, 
tebre. The flesh, being ocean, 
held in place by the great 
pressure of the water, is soft and fragile. The organs of 
touch are often highly developed. The eye is either exces- 
sively large, as if to catch the slightest ray of light, or else 
it is undeveloped, as if the fish had abandoned the effort 
to see. In many cases luminous spots or lanterns are de- 
veloped by which the fish may see to guide his way in the 
al 
