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J. N. BALL AND BRIDGET I. BAKER
axons contain granules varying in size from 100 to 200 mp, together with
much smaller vesicles ( Nishioka and Bern, 1966). In lampreys, the neurohypophysis is merely a slight thickening of the floor of the infundibulum
above the pars intermedia. It is composed of fibers from the NPO (Gorbman, 196!%), many of which terminate around neurohypophysial blood
vessels (van de Kamer and Schreur, 1959) or between the ependymal
cells (Sterba and Bruckner, 1967). There is no evidence of neurohypophysial penetration between the adenohypophysial cells.
Exposure of larval lampreys to continuous light decreased the amount
of neurosecretory material in the NPO and proximal axons, while continuous darkness had the reverse effect (Oztan and Gorbman, 1960).
Neurosecretory material became scarce during metamorphosis of L.
planeri, and AF + ve material completely disappeared during gonad
maturation (van de Kamer and Schreurs, 1959). Sterba and Bruckner
(1967) made ultrastructural studies on the neurohypophysis of L. planeri
after hypothalamic lesions; they found that the axons degenerated, liberating the elementary granules which were phagocytosed by ependymal
cells and then released into the third ventricle. The authors obscurely
interpreted these phenomena as evidence for a normal feedback route
from neurohypophysis to cerebrospinal fluid, as suggested by Knowles
and Vollrath for the eel ( Section 11, C ) .
The blood supply to the cyclostome pituitary, which differs in the two
groups, has been reviewed by Gorbman ( 1965b). In myxinoids, the adenoand neurohypophysis are independently vascularized by branches of the
internal carotid (Gorbman et al., 1963; Gorbman, 196513). In addition, in
Myxine glutinosa the dorsal region of the neurohypophysis receives blood
by a portal vessel from what appears to be a median eminence in the
floor of the hypothalamus just anterior to the pituitary (Olsson, 1959). A
similar portal system has been abserved in the hagfish, Polistotrema,
supplying the neurohypophysis from a neurohemal area just behind the
optic chiasma (Gorbman et al., 1963; Nishioka and Bern, 1966). No
portal vessels or blood from the neurohypophysis seems to supply the
adenohypophysis, the two components being largely separated by connective tissue (Matty, 1960). Blood leaves the adenohypophysis by a
posterior vein which then passes through the neurohypophysis before
leaving the gland. The neurohypophysis is also drained by a more anterior
hypophysial vein.
In the lampreys, the pars distalis has an arterial supply and venous
drainage separate from the neurohypophysis and pars intermedia. Several
small capillaries from the internal carotid enter the pars distalis, and several small venules drain this region. The curious portal supply to the
neurohypophysis seen in the hagfishes is absent from lampreys, this re-
J. N. BALL AND BRIDGET I. BAKER
axons contain granules varying in size from 100 to 200 mp, together with
much smaller vesicles ( Nishioka and Bern, 1966). In lampreys, the neurohypophysis is merely a slight thickening of the floor of the infundibulum
above the pars intermedia. It is composed of fibers from the NPO (Gorbman, 196!%), many of which terminate around neurohypophysial blood
vessels (van de Kamer and Schreur, 1959) or between the ependymal
cells (Sterba and Bruckner, 1967). There is no evidence of neurohypophysial penetration between the adenohypophysial cells.
Exposure of larval lampreys to continuous light decreased the amount
of neurosecretory material in the NPO and proximal axons, while continuous darkness had the reverse effect (Oztan and Gorbman, 1960).
Neurosecretory material became scarce during metamorphosis of L.
planeri, and AF + ve material completely disappeared during gonad
maturation (van de Kamer and Schreurs, 1959). Sterba and Bruckner
(1967) made ultrastructural studies on the neurohypophysis of L. planeri
after hypothalamic lesions; they found that the axons degenerated, liberating the elementary granules which were phagocytosed by ependymal
cells and then released into the third ventricle. The authors obscurely
interpreted these phenomena as evidence for a normal feedback route
from neurohypophysis to cerebrospinal fluid, as suggested by Knowles
and Vollrath for the eel ( Section 11, C ) .
The blood supply to the cyclostome pituitary, which differs in the two
groups, has been reviewed by Gorbman ( 1965b). In myxinoids, the adenoand neurohypophysis are independently vascularized by branches of the
internal carotid (Gorbman et al., 1963; Gorbman, 196513). In addition, in
Myxine glutinosa the dorsal region of the neurohypophysis receives blood
by a portal vessel from what appears to be a median eminence in the
floor of the hypothalamus just anterior to the pituitary (Olsson, 1959). A
similar portal system has been abserved in the hagfish, Polistotrema,
supplying the neurohypophysis from a neurohemal area just behind the
optic chiasma (Gorbman et al., 1963; Nishioka and Bern, 1966). No
portal vessels or blood from the neurohypophysis seems to supply the
adenohypophysis, the two components being largely separated by connective tissue (Matty, 1960). Blood leaves the adenohypophysis by a
posterior vein which then passes through the neurohypophysis before
leaving the gland. The neurohypophysis is also drained by a more anterior
hypophysial vein.
In the lampreys, the pars distalis has an arterial supply and venous
drainage separate from the neurohypophysis and pars intermedia. Several
small capillaries from the internal carotid enter the pars distalis, and several small venules drain this region. The curious portal supply to the
neurohypophysis seen in the hagfishes is absent from lampreys, this re-