26
JERALD J . BERNSTEIN
Therefore, maturity of the nervous system of an animal cannot be
determined by its sexual maturity (Bcrnstein, 1965). The disparity of
results may be because age and species differences are critical in the
ability of fish to reconstitute ablated telcncephalic parenchyma.
IV. DIENCEPHALON
A. Anatomy
Although the diencephalon of fish appears to be extremely variable,
it can be divided into three zones: the epithalamus, thalamus (subdivided into dorsal thalamus and ventral thalamus; Herrick, 1910), and
the hypothalamus. In the elasmobranchs the dorsal thalamus is small and
poorly developed. In the more advanced teleosts the dorsal and ventral
thalamus are not readily separated because of the problem of locating
various sulci that are uscd in order to determinc the homologies of the
different areas ( Nieuwenhuys and Bodenheimer, 1966). In addition, the
various nuclear masses are so varied within teleosts that the picture onc
could gain from homologics is quite confusing and has been revicwcd
elsewhere ( Aronson, 1963; Nieuwenhuys and Bodenheimer, 1966;
Schnitzlcin, 1962 ) .
The epithalamus consists of two parts: (1) the pineal complex and
( 2 ) the habenular nuclei. The pineal organ has been shown to be light
sensitive (Healey, 1957). A conelike photoreceptor has been described
in the parietal eye of the lamprey and many sharks and teleosts and is
presumably the primary sensory receptor ( Altner, 1966; Rertolini and
Mangia, 1966; Breucker and Horstmann, 1965; Eakin, 1963; Rudeberg,
1966, 1968ab). The pineal gland of elasmobranchs consists of three
different cell types (Altner, 1966; Rudeberg, 196%). All authors have
reported that there are sensory cells and supporting cells within the
pineal body. Thc third type of cells, nerve cells, has not been observed
in most studies, but are found in the shark, Scyliorhinus, associated with
rodlike photoreceptors ( Rudeberg, 1968b).
The pineal organ of teleosts contains three differcmt definable cell
types. These are thc sensory, supporting, and ganglion cells. The outer
segments of the photoreceptors arc conelike in teleost fish (Oksche and
Kirschstein, 1967; Rudeberg, 1966, 196th). Ganglion cells have not been
found in all species of teleosts but have been observed in Salmo irirleus
(Y. Morita, 1966) and Oncorhynclrus nerkn (Hafcez and Ford, 1967)
and are prescnt but difficult to demonstrate in Alugil ( Rudeberg, 1968a).
JERALD J . BERNSTEIN
Therefore, maturity of the nervous system of an animal cannot be
determined by its sexual maturity (Bcrnstein, 1965). The disparity of
results may be because age and species differences are critical in the
ability of fish to reconstitute ablated telcncephalic parenchyma.
IV. DIENCEPHALON
A. Anatomy
Although the diencephalon of fish appears to be extremely variable,
it can be divided into three zones: the epithalamus, thalamus (subdivided into dorsal thalamus and ventral thalamus; Herrick, 1910), and
the hypothalamus. In the elasmobranchs the dorsal thalamus is small and
poorly developed. In the more advanced teleosts the dorsal and ventral
thalamus are not readily separated because of the problem of locating
various sulci that are uscd in order to determinc the homologies of the
different areas ( Nieuwenhuys and Bodenheimer, 1966). In addition, the
various nuclear masses are so varied within teleosts that the picture onc
could gain from homologics is quite confusing and has been revicwcd
elsewhere ( Aronson, 1963; Nieuwenhuys and Bodenheimer, 1966;
Schnitzlcin, 1962 ) .
The epithalamus consists of two parts: (1) the pineal complex and
( 2 ) the habenular nuclei. The pineal organ has been shown to be light
sensitive (Healey, 1957). A conelike photoreceptor has been described
in the parietal eye of the lamprey and many sharks and teleosts and is
presumably the primary sensory receptor ( Altner, 1966; Rertolini and
Mangia, 1966; Breucker and Horstmann, 1965; Eakin, 1963; Rudeberg,
1966, 1968ab). The pineal gland of elasmobranchs consists of three
different cell types (Altner, 1966; Rudeberg, 196%). All authors have
reported that there are sensory cells and supporting cells within the
pineal body. Thc third type of cells, nerve cells, has not been observed
in most studies, but are found in the shark, Scyliorhinus, associated with
rodlike photoreceptors ( Rudeberg, 1968b).
The pineal organ of teleosts contains three differcmt definable cell
types. These are thc sensory, supporting, and ganglion cells. The outer
segments of the photoreceptors arc conelike in teleost fish (Oksche and
Kirschstein, 1967; Rudeberg, 1966, 196th). Ganglion cells have not been
found in all species of teleosts but have been observed in Salmo irirleus
(Y. Morita, 1966) and Oncorhynclrus nerkn (Hafcez and Ford, 1967)
and are prescnt but difficult to demonstrate in Alugil ( Rudeberg, 1968a).