182
A. M. PERKS
the neural processes of species of Protopterus are bounded and separated
from the intermedia cells by connective tissue. This connective tissue barrier has been described as a thin membrane in Protopterus annectens
(Wingstrand, 1956,1966) and as a strong sheet in Protopterus aethiopicus
(Kerr and van Oordt, 1966). In Protopterus annectens, a few neurosecretory fibers pass through it into the pars intermedia (Wingstrand, 1956).
The connective tissue investment of the neural processes contains a dense
capillary network ( Protopterus annectenr, Dorn, 1957; Wingstrand, 1966;
P . aethiopicus, Kerr and van Oordt, 1966). If the comments of different
authors are correlated, it seems probable that there is a rich blood supply
through these vessels, although the pars intermedia is often notably avascular ( Lepidosiren sp., Charipper, 1937; Protopterus annectens, Dorn,
1957; Dodd and Kerr, 1963). Further, if the drainage of these vessels is
comparable to that of the similarly located capillaries of the bony fish, it is
possible that they could supply neurosecretory materials to the systemic
circulation.
Clearly, the lungfish pituitary is transitional between that of the fish
and of the tetrapods. It combines an essentially amphibian pattern with a
fishlike intermingling of the pars nervosa and the pars intermedia. However, it is interesting to note that it is most closely related to the pituitary
of the preteleost bony fish; it shares with them a short preoptic nucleus
of comparable location (some species), a median eminence supplied by
a special ventral neurosecretory tract, a pituitary portal system, and large,
well-developed ventricular extensions which penetrate the pars nervosa.
The anatomy of the lungfish pituitary is not only a clue to the evolution
of the tetrapod neurohypophysis, but it is also a reminder of the remarkable degree of specialization which has been developed by the teleost
bony fish.
B. The Nature of the Neurohypophysial Principles of the Dipnoi
The close similarities between the structure of the lungfish and
amphibian pituitary are borne out by the nature of their neurohypophysial peptides. The situation in the lungfish is far from clear, but
their pituitaries may contain arginine vasotocin, 8 Ile oxytocin, and
perhaps oxytocin itself. Follett and Heller (1962, 1963, 1964b) subjected
extracts from the pituitaries of Protopterus aethiopicus and Neoceratodus
forsteri to paper chromatography and separated two active moieties. The
slow-running peak ( Rf approximately 0.3) showed strong vasopressor
activity, and estimations of its oxytocic and natriferic potencies suggested
that it was arginine vasotocin. The fast-running peak ( R f approximately
A. M. PERKS
the neural processes of species of Protopterus are bounded and separated
from the intermedia cells by connective tissue. This connective tissue barrier has been described as a thin membrane in Protopterus annectens
(Wingstrand, 1956,1966) and as a strong sheet in Protopterus aethiopicus
(Kerr and van Oordt, 1966). In Protopterus annectens, a few neurosecretory fibers pass through it into the pars intermedia (Wingstrand, 1956).
The connective tissue investment of the neural processes contains a dense
capillary network ( Protopterus annectenr, Dorn, 1957; Wingstrand, 1966;
P . aethiopicus, Kerr and van Oordt, 1966). If the comments of different
authors are correlated, it seems probable that there is a rich blood supply
through these vessels, although the pars intermedia is often notably avascular ( Lepidosiren sp., Charipper, 1937; Protopterus annectens, Dorn,
1957; Dodd and Kerr, 1963). Further, if the drainage of these vessels is
comparable to that of the similarly located capillaries of the bony fish, it is
possible that they could supply neurosecretory materials to the systemic
circulation.
Clearly, the lungfish pituitary is transitional between that of the fish
and of the tetrapods. It combines an essentially amphibian pattern with a
fishlike intermingling of the pars nervosa and the pars intermedia. However, it is interesting to note that it is most closely related to the pituitary
of the preteleost bony fish; it shares with them a short preoptic nucleus
of comparable location (some species), a median eminence supplied by
a special ventral neurosecretory tract, a pituitary portal system, and large,
well-developed ventricular extensions which penetrate the pars nervosa.
The anatomy of the lungfish pituitary is not only a clue to the evolution
of the tetrapod neurohypophysis, but it is also a reminder of the remarkable degree of specialization which has been developed by the teleost
bony fish.
B. The Nature of the Neurohypophysial Principles of the Dipnoi
The close similarities between the structure of the lungfish and
amphibian pituitary are borne out by the nature of their neurohypophysial peptides. The situation in the lungfish is far from clear, but
their pituitaries may contain arginine vasotocin, 8 Ile oxytocin, and
perhaps oxytocin itself. Follett and Heller (1962, 1963, 1964b) subjected
extracts from the pituitaries of Protopterus aethiopicus and Neoceratodus
forsteri to paper chromatography and separated two active moieties. The
slow-running peak ( Rf approximately 0.3) showed strong vasopressor
activity, and estimations of its oxytocic and natriferic potencies suggested
that it was arginine vasotocin. The fast-running peak ( R f approximately