2. THE PINEAL ORGAN
95
Most of the pineal cells are sensory cells (U. Holmgren, 1959a).
Thesr are most abundant in the vesicular area on the side of the lumen
(Hafeez and Ford, 1967) but occur throughout the pineal epithelium.
These cells are large, ovoid, or club-shaped with well-defined nuclei
surrounded by clear cytoplasm containing many mitochondria and
capped with a membranous structure-an outer segment ( Rudeberg,
1968b). Cytoplasmic outgrowths arising from the sensory cells and
extending into the pineal lumen have also been described (FriedrichFreksa, 1932; Van de Kamer, 1955; Holmgren, 1959a; Hafeez and Ford,
1967). On the pole to the cytoplasmic outgrowths, the sensory cells
give off axons (or the neuraxes of Hafeez and Ford, 1967), which,
together with the dendrites from the ganglion cells (see below), form
a network of axons and dendrites within the pineal organ (U. Holmgren,
1959a).
Supporting cells of various types show a marked affinity for nuclear
stains and lack the typical structure of the sensory cells (U. Holmgren,
19591; Hafeez and Ford, 1967). It is most likely that these cells are of
an ependymal glia type.
Ganglion or nerve cells together with the dendrites and Nissl substance
indicative of their nervous nature, have been described in the pineal
of some but not all fishes examined (U. Holmgren, 1959a; Morita, 1966;
Hafeez and Ford, 1967; Rudeberg, 1968b). Although few in number
compared with the other cell types, ganglion cells may be readily distinguished by their large size and by the presence of two or three wellstained nucleoli ( U . Holmgren, 1959a). Recently, Rudeberg (196813)
has reported that within the pineal of the sardine, Sardina pilchardus
sardinu, the ganglion cells are limited to three small groups. If this
localization of ganglion cells proves to be the case in other fishes, it
may account for the failure of some workers to find pineal ganglion
or nerve cells.
C. Innervation
Apart from the sensory cells proper, afferent nerve fibers connecting
the pineal body with other parts of the brain have been described (Hill,
1894; Studni&ka, 1905; Ariens Kappers, 1965; Rudeberg, 1968b). These
nerves, which appear to represent the axons of ganglion cells ( Rudeberg,
1968b), arise from the extensive nerve net formed within the pineal by
the dendrites of the ganglion cells (U. Holmgren, 1959a) and neuraxis
of the primary sensory cells (Hafeez and Ford, 1967). In the stalk
region, these fibers form variable numbers of nerve bundles (Ariens
95
Most of the pineal cells are sensory cells (U. Holmgren, 1959a).
Thesr are most abundant in the vesicular area on the side of the lumen
(Hafeez and Ford, 1967) but occur throughout the pineal epithelium.
These cells are large, ovoid, or club-shaped with well-defined nuclei
surrounded by clear cytoplasm containing many mitochondria and
capped with a membranous structure-an outer segment ( Rudeberg,
1968b). Cytoplasmic outgrowths arising from the sensory cells and
extending into the pineal lumen have also been described (FriedrichFreksa, 1932; Van de Kamer, 1955; Holmgren, 1959a; Hafeez and Ford,
1967). On the pole to the cytoplasmic outgrowths, the sensory cells
give off axons (or the neuraxes of Hafeez and Ford, 1967), which,
together with the dendrites from the ganglion cells (see below), form
a network of axons and dendrites within the pineal organ (U. Holmgren,
1959a).
Supporting cells of various types show a marked affinity for nuclear
stains and lack the typical structure of the sensory cells (U. Holmgren,
19591; Hafeez and Ford, 1967). It is most likely that these cells are of
an ependymal glia type.
Ganglion or nerve cells together with the dendrites and Nissl substance
indicative of their nervous nature, have been described in the pineal
of some but not all fishes examined (U. Holmgren, 1959a; Morita, 1966;
Hafeez and Ford, 1967; Rudeberg, 1968b). Although few in number
compared with the other cell types, ganglion cells may be readily distinguished by their large size and by the presence of two or three wellstained nucleoli ( U . Holmgren, 1959a). Recently, Rudeberg (196813)
has reported that within the pineal of the sardine, Sardina pilchardus
sardinu, the ganglion cells are limited to three small groups. If this
localization of ganglion cells proves to be the case in other fishes, it
may account for the failure of some workers to find pineal ganglion
or nerve cells.
C. Innervation
Apart from the sensory cells proper, afferent nerve fibers connecting
the pineal body with other parts of the brain have been described (Hill,
1894; Studni&ka, 1905; Ariens Kappers, 1965; Rudeberg, 1968b). These
nerves, which appear to represent the axons of ganglion cells ( Rudeberg,
1968b), arise from the extensive nerve net formed within the pineal by
the dendrites of the ganglion cells (U. Holmgren, 1959a) and neuraxis
of the primary sensory cells (Hafeez and Ford, 1967). In the stalk
region, these fibers form variable numbers of nerve bundles (Ariens