118
A. M. PERKS
secretion between the ependymal cells, to the cerebrospinal fluid (Wingstrand, 1959b; Oztan and Gorbman, 1960a,b; Dodd and Kerr, 1963). This
is not found in the ha$sh. In addition to these connections with the
ventricle above, a few preoptic nerve fibers appear to make direct or
indirect connections with the adenohypophysis below. Roth ( 1956) has
suggested that in adult Petromyzon marinus some nerve fibers which
enter the region close to the preoptic recess may contact capillaries which
supply the adenohypophysis. Oztan and Gorbman ( 196Ob ) have reported
that in the ammocoete larva of the same species, a small number of preoptic fibers terminate in the vascular connective tissue between the rostral adenohypophysis and the brain (Fig. 2). It is even possible that these
fibers, which bear beaded neurosecretory granules, may penetrate the
adenohypophysis itself. In addition, a few preoptic fibers appear to connect with the hindbrain (Fig. 2; Oztan and Gorbman, 1960b). However,
as Roth (1956) has pointed out in Petromyzon marinus, the majority of
the axons of the preoptic cells are directed caudally, toward the pars
nervosa. These axons carry beaded droplets of neurosecretion and form
into a discrete preoptico-hypophysial tract over the rostra1 region of the
adenohypophysis (Dodd and Kerr, 1963). At this point, the tract is relatively avascular, and it is separated from the adenohypophysis by an
almost continuous sheet of connective tissue (Dodd and Kerr, 1963;
Gorbman, 1965). The tract runs within the ventral hypothalamic wall.
This wall is relatively thick and full of neurosecretion in Lampetra
planeri, but in Petromyxon marinus it is thin, and contains few droplets
or nerve endings (Gorbman, 1965). The axons of the preoptico-hypophysial tract terminate caudally in a slightly thickened area of the hypothalamic wall. They enter in a rostro-caudal direction, and also laterally, and
they may be joined by a few axons from neurosecretory cells located in
a posterior hypothalamic nucleus (nucleus lateralis tuberis?) ( Petromyzon marinus, ammocoete; Oztan and Gorbman, 196Ob; Gorbman and
Bern, 1964). In Lampetra planeri the thickened area is broadly continuous with the floor of the brain, but in Petromyxon marinus it has a distinctly globular structure with a central septum at its caudal extremity
(Gorbman, 1965). Although it is not as clearly demarkated as in a mammal, this region may be regarded as the neural lobe or pars nervosa since
it appears to store neurosecretion (Tilney, 1937; Gorbman, 1965). A few
of the neurosecretory axons which enter this region carry beadlike droplets of neurosecretion between the ependymal cells which line the ventricle (Lampetra planeri; van der Kamer and Schreurs, 1959). These
ependymal cells, which contain aldehyde-fuschin-positive granules, send
down processes into the underlying neural tissue and form a structural
lattice for the pars nervosa (Green and Maxwell, 1959; Petromyzon
A. M. PERKS
secretion between the ependymal cells, to the cerebrospinal fluid (Wingstrand, 1959b; Oztan and Gorbman, 1960a,b; Dodd and Kerr, 1963). This
is not found in the ha$sh. In addition to these connections with the
ventricle above, a few preoptic nerve fibers appear to make direct or
indirect connections with the adenohypophysis below. Roth ( 1956) has
suggested that in adult Petromyzon marinus some nerve fibers which
enter the region close to the preoptic recess may contact capillaries which
supply the adenohypophysis. Oztan and Gorbman ( 196Ob ) have reported
that in the ammocoete larva of the same species, a small number of preoptic fibers terminate in the vascular connective tissue between the rostral adenohypophysis and the brain (Fig. 2). It is even possible that these
fibers, which bear beaded neurosecretory granules, may penetrate the
adenohypophysis itself. In addition, a few preoptic fibers appear to connect with the hindbrain (Fig. 2; Oztan and Gorbman, 1960b). However,
as Roth (1956) has pointed out in Petromyzon marinus, the majority of
the axons of the preoptic cells are directed caudally, toward the pars
nervosa. These axons carry beaded droplets of neurosecretion and form
into a discrete preoptico-hypophysial tract over the rostra1 region of the
adenohypophysis (Dodd and Kerr, 1963). At this point, the tract is relatively avascular, and it is separated from the adenohypophysis by an
almost continuous sheet of connective tissue (Dodd and Kerr, 1963;
Gorbman, 1965). The tract runs within the ventral hypothalamic wall.
This wall is relatively thick and full of neurosecretion in Lampetra
planeri, but in Petromyxon marinus it is thin, and contains few droplets
or nerve endings (Gorbman, 1965). The axons of the preoptico-hypophysial tract terminate caudally in a slightly thickened area of the hypothalamic wall. They enter in a rostro-caudal direction, and also laterally, and
they may be joined by a few axons from neurosecretory cells located in
a posterior hypothalamic nucleus (nucleus lateralis tuberis?) ( Petromyzon marinus, ammocoete; Oztan and Gorbman, 196Ob; Gorbman and
Bern, 1964). In Lampetra planeri the thickened area is broadly continuous with the floor of the brain, but in Petromyxon marinus it has a distinctly globular structure with a central septum at its caudal extremity
(Gorbman, 1965). Although it is not as clearly demarkated as in a mammal, this region may be regarded as the neural lobe or pars nervosa since
it appears to store neurosecretion (Tilney, 1937; Gorbman, 1965). A few
of the neurosecretory axons which enter this region carry beadlike droplets of neurosecretion between the ependymal cells which line the ventricle (Lampetra planeri; van der Kamer and Schreurs, 1959). These
ependymal cells, which contain aldehyde-fuschin-positive granules, send
down processes into the underlying neural tissue and form a structural
lattice for the pars nervosa (Green and Maxwell, 1959; Petromyzon