2. THE PINEAL ORGAN
99
rhythm in adult Lampetra. Subsequently, Breder and Rasquin ( 1950),
Hoar (1955), and Schonherr (1955) reported some degree of pigmentary
dispersion after pineal occlusion or destruction-a finding similar to
that reported by Young (1935) in pinealectomized ammocoetes. These
results are supported by the observation that administration of beef
pineal extracts in embryonic and larval Fundulus caused marked pallor
(Wyman, 1924; Fain and Hadley, 1966) although similar results could
not be obtained in adult Fundulus (Fain and Hadley, 1966) or adult
Phoxinus ( Hewer, 1926). The difference in responsiveness between the
young and adults was presumed by Fain and Hadley (1966) to result
from the acquisition, in the adults, of nervous innervation mediated by
catecholamines and a loss of sensitivity to the pineal extracts. Whether
the pallor following pineal extract administration is the result of pituitary
inhibition or a direct action on the pigment cells is not known. A direct
action is, however, suggested by the ability of the pineal extract to
cause pigment concentration in vitro (unpublished).
Photosensitivity of the pineal body has been indirectly demonstrated
in several species of fish by the use of behavioral tests. Breder and
Rasquin (1947), Hoar ( 1955), and Fenwick (1970b) report that phototaxis is abolished following pinealectomy. Further, Breder and Rasquin
(1947) and Fenwick (1970b) found that phototaxis, whether positive or
negative, depended on the presence of intact optic cysts or intact
eyes; they concluded that although the sign of phototaxis was governed
by the pineal organ, the phenomenon itself depended on the presence
of lateral photic receptors. Hoar (1955), however, working with young
sockeye salmon smolts, Oncorh ynchus nerka, found that the negative
phototaxis of otherwise intact animals is not disturbed following damage
to the pineal region; this difference may result from species or age
differences of the animals or differences in the intensity of light employed
in the experiments. The pineal organ of fishes becomes increasingly
invaginated with age (Hoar, 1955) and undergoes a decrease in sensory
cell number with continued development (Hafeez and Ford, 1967)
together with a marked degeneration of nervous elements (Ariens Kappers, 1965). Thus, the pineal body of fishes may change from a primary
photosensory structure in the young fish to a secondary photosensory
structure in the older fish where it can no longer autonomously produce
a phototactic response. On the other hand, Hoar (1955) performed
his experiments outside where the light intensities were much greater
than those employed in other studies (Breder and Rasquin, 1947; Fenwick, 1970b). Previously, von Frisch (1911a) and Young (1935) suggested a general light sensitivity of the diencephalic roof; thus, since
the smolts used by Hoar (1955) had thin skulls, the phototaxis demon-
99
rhythm in adult Lampetra. Subsequently, Breder and Rasquin ( 1950),
Hoar (1955), and Schonherr (1955) reported some degree of pigmentary
dispersion after pineal occlusion or destruction-a finding similar to
that reported by Young (1935) in pinealectomized ammocoetes. These
results are supported by the observation that administration of beef
pineal extracts in embryonic and larval Fundulus caused marked pallor
(Wyman, 1924; Fain and Hadley, 1966) although similar results could
not be obtained in adult Fundulus (Fain and Hadley, 1966) or adult
Phoxinus ( Hewer, 1926). The difference in responsiveness between the
young and adults was presumed by Fain and Hadley (1966) to result
from the acquisition, in the adults, of nervous innervation mediated by
catecholamines and a loss of sensitivity to the pineal extracts. Whether
the pallor following pineal extract administration is the result of pituitary
inhibition or a direct action on the pigment cells is not known. A direct
action is, however, suggested by the ability of the pineal extract to
cause pigment concentration in vitro (unpublished).
Photosensitivity of the pineal body has been indirectly demonstrated
in several species of fish by the use of behavioral tests. Breder and
Rasquin (1947), Hoar ( 1955), and Fenwick (1970b) report that phototaxis is abolished following pinealectomy. Further, Breder and Rasquin
(1947) and Fenwick (1970b) found that phototaxis, whether positive or
negative, depended on the presence of intact optic cysts or intact
eyes; they concluded that although the sign of phototaxis was governed
by the pineal organ, the phenomenon itself depended on the presence
of lateral photic receptors. Hoar (1955), however, working with young
sockeye salmon smolts, Oncorh ynchus nerka, found that the negative
phototaxis of otherwise intact animals is not disturbed following damage
to the pineal region; this difference may result from species or age
differences of the animals or differences in the intensity of light employed
in the experiments. The pineal organ of fishes becomes increasingly
invaginated with age (Hoar, 1955) and undergoes a decrease in sensory
cell number with continued development (Hafeez and Ford, 1967)
together with a marked degeneration of nervous elements (Ariens Kappers, 1965). Thus, the pineal body of fishes may change from a primary
photosensory structure in the young fish to a secondary photosensory
structure in the older fish where it can no longer autonomously produce
a phototactic response. On the other hand, Hoar (1955) performed
his experiments outside where the light intensities were much greater
than those employed in other studies (Breder and Rasquin, 1947; Fenwick, 1970b). Previously, von Frisch (1911a) and Young (1935) suggested a general light sensitivity of the diencephalic roof; thus, since
the smolts used by Hoar (1955) had thin skulls, the phototaxis demon-