2. THE NEUROHYPOPHYSIS
179
and Kerr, 1963; Dodd et aZ., 1966). Recently, Kerr and van Oordt (1966)
have remarked that the intermingling of the pars nervosa and the pars
intermedia in Protopterus aethiopicus is comparable to that of the elasmobranchs and primitive bony fish, so that the lungfish form a good transitional group between the fish and the tetrapods. The general anatomy
of the lungfish pituitary has been clearly described by Wingstrand
(1956), and the neurohypophysial system has been carefully studied by
Dorn (1957), and by Kerr and van Oordt (1966). The recent studies
of Kerr and van Oordt (1966) are the basis of the following general
description of the neurohypophysial system of the Dipnoi.
The preoptic nucleus of Neoceratodus forsteri lies dorsal to the optic
chiasma but rostra1 to the average position found in teleosts. It is one of
the shortest nuclei found in any fish, and Charlton (1932) was impressed
by its general similarity to that of the preteleost bony fish rather than to
the more widespread teleosts. In Protopterus annectens the preoptic
nucleus consists of notably large, bipolar cells, which appear to lie remarkably anterior, and somewhat dorsal to the optic chiasma (Wingstrand, 1956). In both Protopterus annectens and P. aethwpicus, they
contain only a few distinct neurosecretory granules, but in Protopterus
annectens there is also a diffuse general staining of the cytoplasm (Protopterus annectens, Wingstrand, 1956; P. aethwpicus, Kerr and van
Oordt, 1966). The preoptic cells send processes between the ependyma
cells of the ventricle, and these terminate in small globules which are
immersed in the cerebrospinal fluid ( Protopterus annectens, Wingstrand,
1956). The opposite end of the cells gives rise to axons which form the
preoptico-hypophysial tract, which runs first laterally and then ventrocaudally into the walls of the infundibular process (e.g., Protopterus
annectens, Wingstrand, 1956; Dorn, 1957; P. aethiopicus, Kerr and van
Oordt, 1966).
Neoceratodus forsteri ( syn. Epiceratodus), the Australian lungfish,
possesses a distinctive infundibular process; it grows vertically downward
during development so that the pituitary lies a considerable distance ventral to the optic chiasma ( GrifEths, 1938). In species of Lepidosiren, the
South American lungfish, it remains oriented in a ventrocaudal direction
( Dawson, 1940). In Protopterus annectens and P. aethiopicus, the African
lungfish, the infundibulum is a wide, flattened, and well-delimited funnel,
which projects caudally from the floor of the brain; its ventral wall is almost horizontal, and its caudal extremity is divided into two hollow
pockets similiar to those found in the lampreys (Dawson, 1940; Wingstrand, 1966; Kerr and van Oordt, 1966).
In Protoptern annectens, Dorn (1957) has shown that the preoptic
axons are spread widely as they enter the infundibular process, and there
179
and Kerr, 1963; Dodd et aZ., 1966). Recently, Kerr and van Oordt (1966)
have remarked that the intermingling of the pars nervosa and the pars
intermedia in Protopterus aethiopicus is comparable to that of the elasmobranchs and primitive bony fish, so that the lungfish form a good transitional group between the fish and the tetrapods. The general anatomy
of the lungfish pituitary has been clearly described by Wingstrand
(1956), and the neurohypophysial system has been carefully studied by
Dorn (1957), and by Kerr and van Oordt (1966). The recent studies
of Kerr and van Oordt (1966) are the basis of the following general
description of the neurohypophysial system of the Dipnoi.
The preoptic nucleus of Neoceratodus forsteri lies dorsal to the optic
chiasma but rostra1 to the average position found in teleosts. It is one of
the shortest nuclei found in any fish, and Charlton (1932) was impressed
by its general similarity to that of the preteleost bony fish rather than to
the more widespread teleosts. In Protopterus annectens the preoptic
nucleus consists of notably large, bipolar cells, which appear to lie remarkably anterior, and somewhat dorsal to the optic chiasma (Wingstrand, 1956). In both Protopterus annectens and P. aethwpicus, they
contain only a few distinct neurosecretory granules, but in Protopterus
annectens there is also a diffuse general staining of the cytoplasm (Protopterus annectens, Wingstrand, 1956; P. aethwpicus, Kerr and van
Oordt, 1966). The preoptic cells send processes between the ependyma
cells of the ventricle, and these terminate in small globules which are
immersed in the cerebrospinal fluid ( Protopterus annectens, Wingstrand,
1956). The opposite end of the cells gives rise to axons which form the
preoptico-hypophysial tract, which runs first laterally and then ventrocaudally into the walls of the infundibular process (e.g., Protopterus
annectens, Wingstrand, 1956; Dorn, 1957; P. aethiopicus, Kerr and van
Oordt, 1966).
Neoceratodus forsteri ( syn. Epiceratodus), the Australian lungfish,
possesses a distinctive infundibular process; it grows vertically downward
during development so that the pituitary lies a considerable distance ventral to the optic chiasma ( GrifEths, 1938). In species of Lepidosiren, the
South American lungfish, it remains oriented in a ventrocaudal direction
( Dawson, 1940). In Protopterus annectens and P. aethiopicus, the African
lungfish, the infundibulum is a wide, flattened, and well-delimited funnel,
which projects caudally from the floor of the brain; its ventral wall is almost horizontal, and its caudal extremity is divided into two hollow
pockets similiar to those found in the lampreys (Dawson, 1940; Wingstrand, 1966; Kerr and van Oordt, 1966).
In Protoptern annectens, Dorn (1957) has shown that the preoptic
axons are spread widely as they enter the infundibular process, and there