SOME ASPECTS OF I'IIOTORECEPTION AND VISION IN FISHES
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larger in the fish from deeper water. Another subspecies, S.m. marinus,
also from 275 m, had larger cones and smaller rods than S.m. mentelh
from the same depth. These results suggest the existence of intraspecific variation of retinal structure correlated with habitat differences ;
the sample as reported, however, is so small that oonfirmation is
desirable ; dctails concerning size of the fish and time of catches are not
reported.
V. VISUAL PIGMENTS AND SPECTRAL SENSITIVITY
Scotopic visual pigments in great variety have been identified in
fishes : in general, they are of three main types. Rose-coloured pigments
known as rhodopsins are the principal visual pigments in the rods of
I-