1. THE PITUITARY GLAND
83
(Godet, 1962). Under these conditions, the cavities of the intermediate
lobe tubules enlarge.
The dipnoan neurohypophysis is comparable embryologically to the
pars nervosa of tetrapods rather than the neurohypophysis of other fishes
(Wingstrand, 1966a). It consists basically of a system of hollow tubules
of nerve fibers, shown in development to arise as outpushings of the
infundibular cavity, but in the adult this relationship is lost and the
tubules mostly become solid. Ependymal cells, originally surrounding
the tubule cavities, extend in the nervous processes together with abundant AF + ve neurosecretory material (Kerr and van Oordt, 1966). In
the adult, the intertwining of the nervous processes with the cords of the
pars intermedia are very complex. The neural processes contain more
stainable material in aquatic Protopterus than in aerial (estivating) fish,
and the amount of this A F + v e material decreases in fish transferred
from water to aerial cocoons. When air is blown into the mouths of
aquatic fish, there is a marked increase in the amount of neurosecretory
material after 3 hr (Godet, 1960). It is not clear in all these experimental
conditions whether an increase in the amount of material should be taken
to mean increased synthesis or decreased release of the neurohypophysial
principles.
Arginine vasotocin has been identified in the pituitary of Protopterm,
and it has been shown to have diuretic and natriuretic effects when
injected ( Sawyer, 1966a).
Anteriorly, the interdigitating neurohypophysis connects to the thin
floor of the infundibulum which, as in the primitive bony fishes, is separated from the pars distalis by vascular connective tissue (Kerr and van
Oordt, 1966). This region passes at the anterior margin of the gland into
a distinct median eminence, comparable to that of urodele amphibians
( Wingstrand, 1966a). Its capillary plexus is supplied by fibers from the
NPO ( Kerr and van Oordt, 1966), and portal vessels pass from this plexus
to supply the pars distalis ( Wingstrand, 1956,1966a).
V. THE PITUITARY GLAND IN ELASMOBRANCHS
The adenohypophysis in this group is at first sight very unlike that in
other fishes. It is divided into a very large pars intermedia, elaborately
entwined with the neurohypophysis to form a neurointermediate lobe;
and an elongated pars distalis, composed of a dorsal lobe (rostra1 lobe
or anterior lobe) extending forward close beneath the infundibular
floor, and a ventral lobe, attached to the dorsal lobe by a stalk and asso-
83
(Godet, 1962). Under these conditions, the cavities of the intermediate
lobe tubules enlarge.
The dipnoan neurohypophysis is comparable embryologically to the
pars nervosa of tetrapods rather than the neurohypophysis of other fishes
(Wingstrand, 1966a). It consists basically of a system of hollow tubules
of nerve fibers, shown in development to arise as outpushings of the
infundibular cavity, but in the adult this relationship is lost and the
tubules mostly become solid. Ependymal cells, originally surrounding
the tubule cavities, extend in the nervous processes together with abundant AF + ve neurosecretory material (Kerr and van Oordt, 1966). In
the adult, the intertwining of the nervous processes with the cords of the
pars intermedia are very complex. The neural processes contain more
stainable material in aquatic Protopterus than in aerial (estivating) fish,
and the amount of this A F + v e material decreases in fish transferred
from water to aerial cocoons. When air is blown into the mouths of
aquatic fish, there is a marked increase in the amount of neurosecretory
material after 3 hr (Godet, 1960). It is not clear in all these experimental
conditions whether an increase in the amount of material should be taken
to mean increased synthesis or decreased release of the neurohypophysial
principles.
Arginine vasotocin has been identified in the pituitary of Protopterm,
and it has been shown to have diuretic and natriuretic effects when
injected ( Sawyer, 1966a).
Anteriorly, the interdigitating neurohypophysis connects to the thin
floor of the infundibulum which, as in the primitive bony fishes, is separated from the pars distalis by vascular connective tissue (Kerr and van
Oordt, 1966). This region passes at the anterior margin of the gland into
a distinct median eminence, comparable to that of urodele amphibians
( Wingstrand, 1966a). Its capillary plexus is supplied by fibers from the
NPO ( Kerr and van Oordt, 1966), and portal vessels pass from this plexus
to supply the pars distalis ( Wingstrand, 1956,1966a).
V. THE PITUITARY GLAND IN ELASMOBRANCHS
The adenohypophysis in this group is at first sight very unlike that in
other fishes. It is divided into a very large pars intermedia, elaborately
entwined with the neurohypophysis to form a neurointermediate lobe;
and an elongated pars distalis, composed of a dorsal lobe (rostra1 lobe
or anterior lobe) extending forward close beneath the infundibular
floor, and a ventral lobe, attached to the dorsal lobe by a stalk and asso-