174
J . A. C. NICOL
degree. The results suggest that light was acting on some other p h o b
receptors, presumably in the skin.
The responses noted by Breder and RMquin (1950) to stimulation
of the pineal were photokinesis (apparently) and colour change, and
responses of a like nature have been observed in soukeye salmon srnolh
(Hoar, 1955). The smolts showed avoiding reactions (when sttlrtled by
an observer during the day, or by a light at night), negative p h o w
(or photokinesis), and colour-responses (pallor on a white baokground),
Blinded fish showed no avoiding reaction by day, were startled by a
light at night, were negatively phototactic (or photokinetic), and wem
darker than normal fish. Fish lacking pineal organs displayed avoiding
reactions by day and by night ; chromatophore-responses were variable.
Fish blinded and lacking the pineal organ were very dark and were
insensitive to light. The results demonstrate that stimulation of the
pineal area in the salmon smolt influences the movement of pigment in
melanophores and behavioural responses to light. The experiments
involved variable degrees of injury to the pineal organ and to oontiguous regions of the brain in some fish; a minor degree of photosensitivity not connected with the pineal organ and the paired eyes is
not excluded by these experiments. Germane to this work are resulte
obtained on frogs in which action potentials have been recorded from
the pineal nerve after photostimulation (Dodt and Heerd, 1962). The
responses show obvious parallels to those detected in the iish retina
(p. 190), and an extension of this experimental approach to the fiah
pineal would be interesting.
111. REGULATION O F LIGHT ItEACHING SENSORY SUFlFACES
I n fishes which inhabit regions where great diurnal changes of
light-intensities take place, there are usually devicee for controlling the
amount of light reaching the photoreceptors, especially the eyes. We
are concerned here with photomeehanical changes ; equally important,
of course, are those changes in responsiveness of retinal neural elements
and content of visual pigments, which come under the concept of darkadaptation, in its more restricted meaning (Rushton, 1959).
A. Pineal
In many fishes the tissues in the roof of the skull over the pineal
region (Fig. 1 ) are translucent, thus permitting light to reach the pineal
organ and, perhaps, contigupus areas of the brain (see p. 173). Often
there are chromatophores in the skixi over the parietal foramen and, by
their concentration and dispersion, they determine the amount of light
reaching the pineal complex. Experiments involving removal of the
J . A. C. NICOL
degree. The results suggest that light was acting on some other p h o b
receptors, presumably in the skin.
The responses noted by Breder and RMquin (1950) to stimulation
of the pineal were photokinesis (apparently) and colour change, and
responses of a like nature have been observed in soukeye salmon srnolh
(Hoar, 1955). The smolts showed avoiding reactions (when sttlrtled by
an observer during the day, or by a light at night), negative p h o w
(or photokinesis), and colour-responses (pallor on a white baokground),
Blinded fish showed no avoiding reaction by day, were startled by a
light at night, were negatively phototactic (or photokinetic), and wem
darker than normal fish. Fish lacking pineal organs displayed avoiding
reactions by day and by night ; chromatophore-responses were variable.
Fish blinded and lacking the pineal organ were very dark and were
insensitive to light. The results demonstrate that stimulation of the
pineal area in the salmon smolt influences the movement of pigment in
melanophores and behavioural responses to light. The experiments
involved variable degrees of injury to the pineal organ and to oontiguous regions of the brain in some fish; a minor degree of photosensitivity not connected with the pineal organ and the paired eyes is
not excluded by these experiments. Germane to this work are resulte
obtained on frogs in which action potentials have been recorded from
the pineal nerve after photostimulation (Dodt and Heerd, 1962). The
responses show obvious parallels to those detected in the iish retina
(p. 190), and an extension of this experimental approach to the fiah
pineal would be interesting.
111. REGULATION O F LIGHT ItEACHING SENSORY SUFlFACES
I n fishes which inhabit regions where great diurnal changes of
light-intensities take place, there are usually devicee for controlling the
amount of light reaching the photoreceptors, especially the eyes. We
are concerned here with photomeehanical changes ; equally important,
of course, are those changes in responsiveness of retinal neural elements
and content of visual pigments, which come under the concept of darkadaptation, in its more restricted meaning (Rushton, 1959).
A. Pineal
In many fishes the tissues in the roof of the skull over the pineal
region (Fig. 1 ) are translucent, thus permitting light to reach the pineal
organ and, perhaps, contigupus areas of the brain (see p. 173). Often
there are chromatophores in the skixi over the parietal foramen and, by
their concentration and dispersion, they determine the amount of light
reaching the pineal complex. Experiments involving removal of the