98
JAMES CLARKE FENWICK
pineal gland has on the reproductive system of male hamsters. Such
studies have not yet been extended to fishes.
In contrast to the scanty evidence for these pineal functions, many
publications suggest a photosensory role as the primary sensory function of the pineal organ. The evidence, based on a number of fishes,
comes from direct neurophysiological studies as well as indirect evidence
from histology or ultrastructure, color changes, and behavioral tests.
Only the more pertinent evidence will be reviewed here.
By light ( StudniEka, 1905; Dendy, 1907; N. Holmgren, 1920; Adam,
1956, 1957; U. Holmgren, 1959a; Eakin, 1963; Oksche, 1965; Hafeez and
Ford, 1967; Rudeberg, 1968a,b) as well as electron microscopic investigation (Kelly, 1962; Breuker and Horstmann, 1965; Oksche and Vaupel von
Harnak, 1965; Oksche and Kirschstein, 1967; Riid:*berg, 1966), it has been
clearly demonstrated that morphologically the neurosensory cells present
in the epithelium of the pineal body are very similar to the ciliary type of
photosensory cells present in the retina of the lateral eyes ( Ariens Kappers,
1965) and possess characteristics which are indisputably conelike ( Brcuker
and Horstmann, 1965; Oksche and Kirschstein, 1967). It has been suggested by Dc la Mottc (1963) that the light receptive role of the pineal
body in Phoxintrs is based on porphyropsin, although Thines and Kahling
(1957) had prcviously reported a different visual pigment in Anoptichthys. More directly, Gruncwald-Lowenstein ( 1956) observed histological and histochemical changes in the pineal organ of Astannx
following prolonged exposure to continuous darkness or illumination.
Similar changes, however, were not found in young sockeye salmon held
under different light regimes (Hafeez and Ford, 1967). Recently, Dodt
(1963) and Morita (1966) have demonstrated the photosensory potential
of the fish pineal by electrophysiologically detecting alterations in nervous activity in the pincal of Salmo irideus during and after illumination
of the pineal even though this species lacks any specializcd tissue overlying the pineal organ. This finding is important when attempting to
define a light receptive role for the pineal in those fishes which possess
apparently light impermeable skulls. It questions the theory that such
a skull precludes a photosensory role.
A light receptive role of the pineal organ is also indicated by lightinduced alterations of pigment distribution within the chromatophores.
Although several studics suggested that the pineal had no effect on
pigment distribution (von Frisch, 1911a,b; Scharrer, 1927; Wykes, 1938),
von Frisch did find that some part of the diencephalon was involved
in chromatophore responses. The pineal was more directly implicated
by Young (1935) who found that pineal extirpation abolished the marked
diurnal rhythm of color change in ammocoetes and distributed the
JAMES CLARKE FENWICK
pineal gland has on the reproductive system of male hamsters. Such
studies have not yet been extended to fishes.
In contrast to the scanty evidence for these pineal functions, many
publications suggest a photosensory role as the primary sensory function of the pineal organ. The evidence, based on a number of fishes,
comes from direct neurophysiological studies as well as indirect evidence
from histology or ultrastructure, color changes, and behavioral tests.
Only the more pertinent evidence will be reviewed here.
By light ( StudniEka, 1905; Dendy, 1907; N. Holmgren, 1920; Adam,
1956, 1957; U. Holmgren, 1959a; Eakin, 1963; Oksche, 1965; Hafeez and
Ford, 1967; Rudeberg, 1968a,b) as well as electron microscopic investigation (Kelly, 1962; Breuker and Horstmann, 1965; Oksche and Vaupel von
Harnak, 1965; Oksche and Kirschstein, 1967; Riid:*berg, 1966), it has been
clearly demonstrated that morphologically the neurosensory cells present
in the epithelium of the pineal body are very similar to the ciliary type of
photosensory cells present in the retina of the lateral eyes ( Ariens Kappers,
1965) and possess characteristics which are indisputably conelike ( Brcuker
and Horstmann, 1965; Oksche and Kirschstein, 1967). It has been suggested by Dc la Mottc (1963) that the light receptive role of the pineal
body in Phoxintrs is based on porphyropsin, although Thines and Kahling
(1957) had prcviously reported a different visual pigment in Anoptichthys. More directly, Gruncwald-Lowenstein ( 1956) observed histological and histochemical changes in the pineal organ of Astannx
following prolonged exposure to continuous darkness or illumination.
Similar changes, however, were not found in young sockeye salmon held
under different light regimes (Hafeez and Ford, 1967). Recently, Dodt
(1963) and Morita (1966) have demonstrated the photosensory potential
of the fish pineal by electrophysiologically detecting alterations in nervous activity in the pincal of Salmo irideus during and after illumination
of the pineal even though this species lacks any specializcd tissue overlying the pineal organ. This finding is important when attempting to
define a light receptive role for the pineal in those fishes which possess
apparently light impermeable skulls. It questions the theory that such
a skull precludes a photosensory role.
A light receptive role of the pineal organ is also indicated by lightinduced alterations of pigment distribution within the chromatophores.
Although several studics suggested that the pineal had no effect on
pigment distribution (von Frisch, 1911a,b; Scharrer, 1927; Wykes, 1938),
von Frisch did find that some part of the diencephalon was involved
in chromatophore responses. The pineal was more directly implicated
by Young (1935) who found that pineal extirpation abolished the marked
diurnal rhythm of color change in ammocoetes and distributed the