128
A. M. PERKS
(Perks, 1959). In 1962, Braak was able to trace the neurosecretory tracts
of Spinax niger by the elegant technique of staining and clearing whole
mounts. In the following year, Knowles (1963) applied electron microscopy to the study of the diffuse neural lobe of Scylwrhinus stellurw.
However, the most important advance of recent years has been the demonstration of a hypothalamo-hypophysial portal system in the elasmobranch pituitary ( Meurling, 1960; Mellinger, 1960). Meurling ( 1962,
1963, 1967a) has made careful comparisons of both the portal system and
the neurohypophysis in different species, and the following general description is based largely on his excellent work.
The preoptic nucleus of the elasmobranchs is found dorsal to the optic
chiasma and close to the ependymal lining of the ventricle (Fig. 4). It is
shorter than that of most teleosts, and its position vanes from being relatively rostra1 in the sharks (especially in Squalus acanthias), to being
remarkedly caudal in the skates ( Charlton, 1932; Meurling, 1967a). The
cells are often found lying with their long axes parallel to the ventricular
lining ( Scyliorhinus caniculus; Perks, 1959). They are relatively uniform
in size, and there is no division into a pars magnocellularis and a pars
parvocellularis, as seen in the teleosts (Charlton, 1932). The preoptic
cells are usually large and distinct, as in Etmopterus spinax and Scyliorhinus caniculus, but in some species such as Squulus acanthias they are
less well marked (Scharrer, 1952; Meurling, 1967a). They contain innumerable small granules, which stain by Gomori’s chrome-hematoxylinphloxin method, and by other so-called neurosecretory stains (e.g.,
Scy2iorhinus stellark; Scharrer, 1952). The droplets appear to contain a
high sulfur content ( Scyliorhinus caniculus; Perks, 1959). In Scyliorhinus
caniculus there is a great variation in the amount of neurosecretion present in the preoptic nucleus, and indeed, throughout the entire neurohypophysis. If the neurointermediate lobe of the pituitary is removed, or
the preoptico-hypophysial tract is cut, the preoptic nucleus becomes completely empty of neurosecretory granules ( Scyliorhinus caniculus; Perks,
1959; Mellinger, 1963a). In normal specimens different cells within the
same nucleus appear to be in different stages of secretion (Scyliorhinus
caniculus, Mazzi, 1952; Scyliorhinus stellaris, Scharrer, 1962). Studies
with the light microscope have suggested that neurosecretory granules
appear in the walls of peripheral cytoplasmic vacuoles, and then spread
throughout the cytoplasm, becoming particularly dense in the poles of
the cells (Scyliorhinus caniculus, Mazzi, 1952; Perks, 1959: S . stellurk,
Scharrer, 1952). Beads of neurosecretion can be found in dendrites which
pass to the third ventricle, but most appear to leave the cells along the
thick cellular processes, which narrow down to form the unmyelinated
fibers of the preoptico-hypophysial tract ( Scyliorhinus caniculus, Mazzi,
1952; S . stellark, Scharrer, 1952). The axons of this tract run down behind the optic chiasma in a diffuse manner; at first they lack neurosecre-
A. M. PERKS
(Perks, 1959). In 1962, Braak was able to trace the neurosecretory tracts
of Spinax niger by the elegant technique of staining and clearing whole
mounts. In the following year, Knowles (1963) applied electron microscopy to the study of the diffuse neural lobe of Scylwrhinus stellurw.
However, the most important advance of recent years has been the demonstration of a hypothalamo-hypophysial portal system in the elasmobranch pituitary ( Meurling, 1960; Mellinger, 1960). Meurling ( 1962,
1963, 1967a) has made careful comparisons of both the portal system and
the neurohypophysis in different species, and the following general description is based largely on his excellent work.
The preoptic nucleus of the elasmobranchs is found dorsal to the optic
chiasma and close to the ependymal lining of the ventricle (Fig. 4). It is
shorter than that of most teleosts, and its position vanes from being relatively rostra1 in the sharks (especially in Squalus acanthias), to being
remarkedly caudal in the skates ( Charlton, 1932; Meurling, 1967a). The
cells are often found lying with their long axes parallel to the ventricular
lining ( Scyliorhinus caniculus; Perks, 1959). They are relatively uniform
in size, and there is no division into a pars magnocellularis and a pars
parvocellularis, as seen in the teleosts (Charlton, 1932). The preoptic
cells are usually large and distinct, as in Etmopterus spinax and Scyliorhinus caniculus, but in some species such as Squulus acanthias they are
less well marked (Scharrer, 1952; Meurling, 1967a). They contain innumerable small granules, which stain by Gomori’s chrome-hematoxylinphloxin method, and by other so-called neurosecretory stains (e.g.,
Scy2iorhinus stellark; Scharrer, 1952). The droplets appear to contain a
high sulfur content ( Scyliorhinus caniculus; Perks, 1959). In Scyliorhinus
caniculus there is a great variation in the amount of neurosecretion present in the preoptic nucleus, and indeed, throughout the entire neurohypophysis. If the neurointermediate lobe of the pituitary is removed, or
the preoptico-hypophysial tract is cut, the preoptic nucleus becomes completely empty of neurosecretory granules ( Scyliorhinus caniculus; Perks,
1959; Mellinger, 1963a). In normal specimens different cells within the
same nucleus appear to be in different stages of secretion (Scyliorhinus
caniculus, Mazzi, 1952; Scyliorhinus stellaris, Scharrer, 1962). Studies
with the light microscope have suggested that neurosecretory granules
appear in the walls of peripheral cytoplasmic vacuoles, and then spread
throughout the cytoplasm, becoming particularly dense in the poles of
the cells (Scyliorhinus caniculus, Mazzi, 1952; Perks, 1959: S . stellurk,
Scharrer, 1952). Beads of neurosecretion can be found in dendrites which
pass to the third ventricle, but most appear to leave the cells along the
thick cellular processes, which narrow down to form the unmyelinated
fibers of the preoptico-hypophysial tract ( Scyliorhinus caniculus, Mazzi,
1952; S . stellark, Scharrer, 1952). The axons of this tract run down behind the optic chiasma in a diffuse manner; at first they lack neurosecre-