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A. M. PERKS
abolished. It is clear that further work is needed to clarify the true significance of the close relations.hip between the neurosecretory fibers and
the intermedia cells.
IV. CARTILAGINOUS FISH: THE HOLOCEPHALIANS
A. The Structure of the Neurohypophysis of the Holocephalians
This ancient group of cartilaginous fish occupies a puzzling position
in the evolutionary series. Its members are of particular interest because
in some ways they may be intermediate between the elasmobranchs and
the bony fish.
The holocephalians have a flask-shaped pituitary which recalls that of
the elasmobranchs: this can be seen by comparing Figs. 4 and 5 (Hydrolagus colliei, Sathyanesan, 1965a; Chimera monstrosa, Dodd and Kerr,
1963). However, it has an individuality of its own. Fujita (1963), working in Chimaera monstrosa, recognized the presence of a unique and only
partly formed neurohypophysial system in which the neurosecretory cells
were located in the neurointermediate lobe, but this was not confirmed
by Altner ( 1966), who found a complete preoptico-hypophysial system
in the same species. It is possible that the relative absence of neurosecretory material noted by Fujita (1963) may have been a reflection of some
physiological or pathological state, since Sathyanesan ( 1965a ) and Jasinski and Gorbman (1966) have demonstrated a well-defined neurohypophysial system, rich in neurosecretion, in the related species, Hydrolagzls
colliei (Fig. 5). The following general description of the neurohypophysis
of Hydrolagus colliei is based on the work of these investigators.
In Hydrolagus collki, the preoptic nucleus lies anterodorsal to the
optic chiasma, in a location similar to that of the elasmobranchs (Fig. 5 ) .
It is diffuse in form but highly vascularized. The cells are irregular in
shape, larger than those of elasmobranchs, and not divided by size into
magnocellular or parvocellular varieties, as in the teleosts. The preoptic
cells contain intensely staining, aldehyde-fuchsin-positive neurosecretory
material. A few cells send beaded axons toward the forebrain (Sathyanesan, 1965a), but the majority give rise to two groups of notably wide
axons, which unite behind the optic chiasma to form a single preopticohypophysial tract. This tract is rich in neurosecretion, and accumulations
similar to Herring bodies are found even in the preoptic region. The tract
passes in a caudal direction, and runs below the elongated nucleus lateralis tuberis, which also contains aldehyde-fuchsin-positive material
(Fig. 5). In this region, the preoptico-hypophysial tract gives off ventral
A. M. PERKS
abolished. It is clear that further work is needed to clarify the true significance of the close relations.hip between the neurosecretory fibers and
the intermedia cells.
IV. CARTILAGINOUS FISH: THE HOLOCEPHALIANS
A. The Structure of the Neurohypophysis of the Holocephalians
This ancient group of cartilaginous fish occupies a puzzling position
in the evolutionary series. Its members are of particular interest because
in some ways they may be intermediate between the elasmobranchs and
the bony fish.
The holocephalians have a flask-shaped pituitary which recalls that of
the elasmobranchs: this can be seen by comparing Figs. 4 and 5 (Hydrolagus colliei, Sathyanesan, 1965a; Chimera monstrosa, Dodd and Kerr,
1963). However, it has an individuality of its own. Fujita (1963), working in Chimaera monstrosa, recognized the presence of a unique and only
partly formed neurohypophysial system in which the neurosecretory cells
were located in the neurointermediate lobe, but this was not confirmed
by Altner ( 1966), who found a complete preoptico-hypophysial system
in the same species. It is possible that the relative absence of neurosecretory material noted by Fujita (1963) may have been a reflection of some
physiological or pathological state, since Sathyanesan ( 1965a ) and Jasinski and Gorbman (1966) have demonstrated a well-defined neurohypophysial system, rich in neurosecretion, in the related species, Hydrolagzls
colliei (Fig. 5). The following general description of the neurohypophysis
of Hydrolagus colliei is based on the work of these investigators.
In Hydrolagus collki, the preoptic nucleus lies anterodorsal to the
optic chiasma, in a location similar to that of the elasmobranchs (Fig. 5 ) .
It is diffuse in form but highly vascularized. The cells are irregular in
shape, larger than those of elasmobranchs, and not divided by size into
magnocellular or parvocellular varieties, as in the teleosts. The preoptic
cells contain intensely staining, aldehyde-fuchsin-positive neurosecretory
material. A few cells send beaded axons toward the forebrain (Sathyanesan, 1965a), but the majority give rise to two groups of notably wide
axons, which unite behind the optic chiasma to form a single preopticohypophysial tract. This tract is rich in neurosecretion, and accumulations
similar to Herring bodies are found even in the preoptic region. The tract
passes in a caudal direction, and runs below the elongated nucleus lateralis tuberis, which also contains aldehyde-fuchsin-positive material
(Fig. 5). In this region, the preoptico-hypophysial tract gives off ventral