154
A. M. PERKS
fibers run below the nucleus lateralis tuberis in Amia calva and through
it in Lepidosteus osseus. The nucleus lateralis tuberis is much more extensive in the holosteans than in other preteleost fish, and it may add its
own fibers to the tract. These are also bound for the pituitary (Amia
calva, Lepidosteus osseus; Charlton, 1932; Sathyanesan and Chavin,
1967). The preoptico-hypophysial tract which runs in the infundibular
floor is rich in beaded droplets of neurosecretion and in Herring bodies.
In Amia calva, the amount of stainable material is equivalent to that
found in the pars nervosa-so great, in fact, that Sathyanesan and Chavin
(1967) have suggested that the infundibular wall and the pars nervosa
form a continuous functional unit. In Amia calua, Lepidosteus osseus, and
L. platostomus, neurosecretory material has been seen in close association
with blood vessels which penetrate the wall of the infundibulum. Frequently, Herring bodies surround these invading capillaries. The capillaries drain through the underlying connective tissue into the rostral
region of the adenohypophysis. In the case of Amia calva, the dividing
connective tissue is particularly thin, and the blood vessels which pass
through it form wide sinusoids. These observations strongly suggest that
the holosteans possess a simple median eminence and pituitary portal
system, and this is in marked contrast to the situation in the teleost fish
(Dodd and Kerr, 1963; Sathyanesan and Chavin, 1967).
Many of the axons of the preoptico-hypophysial tract do not terminate
on the infundibular blood vessels, but pass caudally, to form the pars
nervosa. In Lepidosteus osseus and L. pidostomus, there is no sign of a
hypophysial stalk, and the ventral infundibular wall remains relatively
flat throughout its length. The pars nervosa is formed by many hollow
or solid neural processes, which grow downward and laterally from the
caudal region of the infundibular floor. These processes penetrate the
tissue of the pars intermedia, which is confined to the caudal region of
the elongated pituitary (Green, 1951; Dodd and Kerr, 1963; Sathyanesan
and Chavin, 1967). The general form is reminiscent of that seen in other
preteleost groups, particularly in the sturgeons. In Amia calua, the general
shape is different, but the essential relationships are similar (Dodd and
Kerr, 1963). In this species, the infundibular wall folds outward to form
a funnel which projects in a rostral direction below the optic chiasma
and intrudes into the pars intermedia. Fingerlike processes arise from
the funnel and ramify between the intermedia cells; unlike the neural
intrusions of the teleosts, these processes are confined to the pars intermedia tissue (Dodd and Kerr, 1963; Sathyanesan and Chavin, 1967). The
processes of the pars nervosa contain a few large, argyrophylic ganglion
cells, but they are more notable for their rich accumulation of neurosecretory granules and Herring bodies (Lepidosteus osseus, Amia calua; Green,
1951, Dodd and Kerr, 1963). In Lepidosteus osseus, the neurosecretory
A. M. PERKS
fibers run below the nucleus lateralis tuberis in Amia calva and through
it in Lepidosteus osseus. The nucleus lateralis tuberis is much more extensive in the holosteans than in other preteleost fish, and it may add its
own fibers to the tract. These are also bound for the pituitary (Amia
calva, Lepidosteus osseus; Charlton, 1932; Sathyanesan and Chavin,
1967). The preoptico-hypophysial tract which runs in the infundibular
floor is rich in beaded droplets of neurosecretion and in Herring bodies.
In Amia calva, the amount of stainable material is equivalent to that
found in the pars nervosa-so great, in fact, that Sathyanesan and Chavin
(1967) have suggested that the infundibular wall and the pars nervosa
form a continuous functional unit. In Amia calua, Lepidosteus osseus, and
L. platostomus, neurosecretory material has been seen in close association
with blood vessels which penetrate the wall of the infundibulum. Frequently, Herring bodies surround these invading capillaries. The capillaries drain through the underlying connective tissue into the rostral
region of the adenohypophysis. In the case of Amia calva, the dividing
connective tissue is particularly thin, and the blood vessels which pass
through it form wide sinusoids. These observations strongly suggest that
the holosteans possess a simple median eminence and pituitary portal
system, and this is in marked contrast to the situation in the teleost fish
(Dodd and Kerr, 1963; Sathyanesan and Chavin, 1967).
Many of the axons of the preoptico-hypophysial tract do not terminate
on the infundibular blood vessels, but pass caudally, to form the pars
nervosa. In Lepidosteus osseus and L. pidostomus, there is no sign of a
hypophysial stalk, and the ventral infundibular wall remains relatively
flat throughout its length. The pars nervosa is formed by many hollow
or solid neural processes, which grow downward and laterally from the
caudal region of the infundibular floor. These processes penetrate the
tissue of the pars intermedia, which is confined to the caudal region of
the elongated pituitary (Green, 1951; Dodd and Kerr, 1963; Sathyanesan
and Chavin, 1967). The general form is reminiscent of that seen in other
preteleost groups, particularly in the sturgeons. In Amia calua, the general
shape is different, but the essential relationships are similar (Dodd and
Kerr, 1963). In this species, the infundibular wall folds outward to form
a funnel which projects in a rostral direction below the optic chiasma
and intrudes into the pars intermedia. Fingerlike processes arise from
the funnel and ramify between the intermedia cells; unlike the neural
intrusions of the teleosts, these processes are confined to the pars intermedia tissue (Dodd and Kerr, 1963; Sathyanesan and Chavin, 1967). The
processes of the pars nervosa contain a few large, argyrophylic ganglion
cells, but they are more notable for their rich accumulation of neurosecretory granules and Herring bodies (Lepidosteus osseus, Amia calua; Green,
1951, Dodd and Kerr, 1963). In Lepidosteus osseus, the neurosecretory