2. THE NEUROHYPOPHYSIS
151
The majority of the axons of the preoptico-hypophysial tract continue
caudally in the infundibular walf and spread out into a broad, thin bundle.
At the end of the infundibular process, this neural lamella gives rise to
large, hollow diverticuli and occasional solid processes, which form on
either side of the midline (Fig. 7). These protrusions branch and penetrate into the underlying intermedia tissue, and they constitute the pars
nervosa (Pickford and Atz, 1957; Acipenser ruthenus, Dodd and Kerr,
1963; A. guldenstadti Brandt, A. stellatus Pallas, HMO huso L., Polenov
and Barannikova, 1958). The pars nervosa is similar in form to that of
the primitive brachiopterygian bony fish. Its penetration of the adenohypophysis is strictly restricted to the pars intermedia by the persistent
adenohypophysial cavity, into which the neurointermediate complex protrudes (Acipenser stellatus Pallas, Jasinski, 1964; see also, Fig. 7 ) . This
primitive situation contrasts with the extensive general penetration found
in the teleost fish. The pars nervosa of the Chondrostei contains large
Herring bodies in which a central neural structure can be distinguished.
These neurosecretory bodies are found in the tissues of the tubelike neural
processes, within their ependymal lining, and even inside their central
ventricular cavities. They also occur beneath the endothelial linings of
the sinusoidal capillaries which cover the surface of the neural processes
( Acipenser guldenstadti Brandt, A. stellatus Pallas, Huso hwo L., Polenov
and Barannikova, 1958). These capillaries drain into veins which are
separate from those of the rest of the pituitary, and empty through the
cerebri media veins into the general circulation ( Acipenser stellatus,
Pallas, Jasinski, 1964). It appears that neurohypophysial material could
reach the rostra1 adenohypophysis through the primitive portal system,
and it could also reach the general circulation through the sinuses of the
neurointermediate lobe.
B. The Nature of the Neurohypophysial Principles of the Chondrostei
The neurohypophysial principles of a number of Chondrosteans have
received preliminary study by pharmacological methods ( Polydon spathula, Acipenser guMemtadti persicus Boradin, A. guldenstadti Brandt,
and A. nudiuentris; Follett and Heller, 1964a). The levels of oxytocic and
vasopressor activity detected in the pituitaries of Polydon spathula suggested that they contained only arginine vasotocin, and this was supported by the failure of paper chromatography to resolve a neutral
principle. However, any neutral peptide accounting for less than 6% of
the total oxytocic activity would have escaped detection (Follett and
Heller, 1964a). This is a serious possibility, since extracts from species
of Acipenser were subjected to paper chromatography and contained a
151
The majority of the axons of the preoptico-hypophysial tract continue
caudally in the infundibular walf and spread out into a broad, thin bundle.
At the end of the infundibular process, this neural lamella gives rise to
large, hollow diverticuli and occasional solid processes, which form on
either side of the midline (Fig. 7). These protrusions branch and penetrate into the underlying intermedia tissue, and they constitute the pars
nervosa (Pickford and Atz, 1957; Acipenser ruthenus, Dodd and Kerr,
1963; A. guldenstadti Brandt, A. stellatus Pallas, HMO huso L., Polenov
and Barannikova, 1958). The pars nervosa is similar in form to that of
the primitive brachiopterygian bony fish. Its penetration of the adenohypophysis is strictly restricted to the pars intermedia by the persistent
adenohypophysial cavity, into which the neurointermediate complex protrudes (Acipenser stellatus Pallas, Jasinski, 1964; see also, Fig. 7 ) . This
primitive situation contrasts with the extensive general penetration found
in the teleost fish. The pars nervosa of the Chondrostei contains large
Herring bodies in which a central neural structure can be distinguished.
These neurosecretory bodies are found in the tissues of the tubelike neural
processes, within their ependymal lining, and even inside their central
ventricular cavities. They also occur beneath the endothelial linings of
the sinusoidal capillaries which cover the surface of the neural processes
( Acipenser guldenstadti Brandt, A. stellatus Pallas, Huso hwo L., Polenov
and Barannikova, 1958). These capillaries drain into veins which are
separate from those of the rest of the pituitary, and empty through the
cerebri media veins into the general circulation ( Acipenser stellatus,
Pallas, Jasinski, 1964). It appears that neurohypophysial material could
reach the rostra1 adenohypophysis through the primitive portal system,
and it could also reach the general circulation through the sinuses of the
neurointermediate lobe.
B. The Nature of the Neurohypophysial Principles of the Chondrostei
The neurohypophysial principles of a number of Chondrosteans have
received preliminary study by pharmacological methods ( Polydon spathula, Acipenser guMemtadti persicus Boradin, A. guldenstadti Brandt,
and A. nudiuentris; Follett and Heller, 1964a). The levels of oxytocic and
vasopressor activity detected in the pituitaries of Polydon spathula suggested that they contained only arginine vasotocin, and this was supported by the failure of paper chromatography to resolve a neutral
principle. However, any neutral peptide accounting for less than 6% of
the total oxytocic activity would have escaped detection (Follett and
Heller, 1964a). This is a serious possibility, since extracts from species
of Acipenser were subjected to paper chromatography and contained a