76
J. N. BALL A N D BRIDGET I. BAKER
clearly separated by the fact that Type 1 is -ve and Type 2 +ve to AF
without oxidation. There are unfortunately no grounds for allocating
functions to these various cells. In the pars intermedia, Kerr described a
single PAS + ve basophil, arranged in cords around the complex processes of the neurohypophysis. The PbH-PAS technique confirms that the
pars intermedia of Calamoichthys contains a single cell type, PAS + ve
but PbH - ve (Ball, 1968).
The pars intermedia is the only part of the adenohypophysis to be
invaded by neurohypophysial processes, although Kerr (1968) did see a
single instance in which a short process of nervous tissue, laden with
neurosecretory granules, projected a little way into the proximal pars distalis, perhaps a “foreshadowing” of the teleostean condition. In the pars
intermedia region the inpushings of the neurohypophysis are hollow, the
lumen communicating with the third ventricle and lined by ependymal
cells (pituicytes), recalling the arrangement in the eel (Section 11, C, 1).
Cords of ependymal cells extend beyond the lumen in the middle of the
distal nervous processes. The neurohypophysis contains typical stainable
neurosecretory material, apparently derived from the NPO. A main tract
of fibers from the NPO leads into the neurohypophysial core, and the
stainable material can be seen to concentrate close to the pars intermedia
cells. Lagios (1968) showed that fibers in this region also contact capillary
walls.
A subsidiary tract from the NPO lies ventral to the main tract in the
hypothalamic floor and shows prominent stainable material just anterior
to the tip of the pituitary. In this region the neurosecretory fibers are
closely mingled with a plexus of blood capillaries, and branches from this
plexus pass into the pars distalis across a connective tissue pad at the
front end of the gland (Fig. 25E). As Kerr (1968) pointed out, there
is little reason to doubt that here we have a typical median eminence and
extrapituitary portal system. This is confirmed by ultrastructural studies,
which showed that in the median eminence of Calamoichthys there are
neurosecretory fibers with granules 100-150 mp diam which terminate on
extravascular spaces around capillaries in a manner indistinguishable
from that in the amphibian median eminence (Lagios, 1968). According
to Lagios, the portal vessels contribute the sole vascular supply to the
pituitary of Calamoichthys, but Kerr (1968) thought that part of the rich
vascular plexus in the neurohypophysial tracts in the pars intermedia of
Polypterus and Calamoichthys derived from vessels in the wall of the
brain.
In addition to the portal vessels in the connective tissue pad, the connective tissue sheet between the pars distalis and the infundibular floor
( = anterior part of neurohypophysis) is highly vascular, and its capil-
J. N. BALL A N D BRIDGET I. BAKER
clearly separated by the fact that Type 1 is -ve and Type 2 +ve to AF
without oxidation. There are unfortunately no grounds for allocating
functions to these various cells. In the pars intermedia, Kerr described a
single PAS + ve basophil, arranged in cords around the complex processes of the neurohypophysis. The PbH-PAS technique confirms that the
pars intermedia of Calamoichthys contains a single cell type, PAS + ve
but PbH - ve (Ball, 1968).
The pars intermedia is the only part of the adenohypophysis to be
invaded by neurohypophysial processes, although Kerr (1968) did see a
single instance in which a short process of nervous tissue, laden with
neurosecretory granules, projected a little way into the proximal pars distalis, perhaps a “foreshadowing” of the teleostean condition. In the pars
intermedia region the inpushings of the neurohypophysis are hollow, the
lumen communicating with the third ventricle and lined by ependymal
cells (pituicytes), recalling the arrangement in the eel (Section 11, C, 1).
Cords of ependymal cells extend beyond the lumen in the middle of the
distal nervous processes. The neurohypophysis contains typical stainable
neurosecretory material, apparently derived from the NPO. A main tract
of fibers from the NPO leads into the neurohypophysial core, and the
stainable material can be seen to concentrate close to the pars intermedia
cells. Lagios (1968) showed that fibers in this region also contact capillary
walls.
A subsidiary tract from the NPO lies ventral to the main tract in the
hypothalamic floor and shows prominent stainable material just anterior
to the tip of the pituitary. In this region the neurosecretory fibers are
closely mingled with a plexus of blood capillaries, and branches from this
plexus pass into the pars distalis across a connective tissue pad at the
front end of the gland (Fig. 25E). As Kerr (1968) pointed out, there
is little reason to doubt that here we have a typical median eminence and
extrapituitary portal system. This is confirmed by ultrastructural studies,
which showed that in the median eminence of Calamoichthys there are
neurosecretory fibers with granules 100-150 mp diam which terminate on
extravascular spaces around capillaries in a manner indistinguishable
from that in the amphibian median eminence (Lagios, 1968). According
to Lagios, the portal vessels contribute the sole vascular supply to the
pituitary of Calamoichthys, but Kerr (1968) thought that part of the rich
vascular plexus in the neurohypophysial tracts in the pars intermedia of
Polypterus and Calamoichthys derived from vessels in the wall of the
brain.
In addition to the portal vessels in the connective tissue pad, the connective tissue sheet between the pars distalis and the infundibular floor
( = anterior part of neurohypophysis) is highly vascular, and its capil-