68
J. N. BALL AND BRIDGET I. BAKER
most striking characteristic of the blood supply to the gland is that the
blood reaching the adenohypophysis has passed through capillaries in the
neurohypophysis; and further, there is no independent venous drainage
of the neurohypophysis apart perhaps from a posterior connection to the
hypophysial vein in some species (Follenius and Porte, 1962). In these
respects, the vascularization of the fish gland differs greatly from the
tetrapod condition (Wingstrand, 1959, 1966a; Green and Maxwell, 1959;
Green, 1W6).
Most students of the subject have described a collection of capillaries in the neurohypophysis, forming a vascular plexus in the neurohypophysial core, close to the adenohypophysial boundary ( e.g., cyprinodonts, Follenius, 1963a,b), or actually at the neuro-adeno interface
( several species, Jasinski, 1961, 1962). This plexus in the neurohypophysis
is the primary longitudinal plexus or system of Follenius (1965a,b; Fig.
24). In the adult Phoxinus, and no doubt in other species, it includes a
large central longitudinal sinus ( Bhargava, 1966). From this plexus a
series of capillaries passes into the adenohypophysis and forms an
elaborate network of capillaries and sinuses between the endocrine cells;
Follenius ( 1965a,b ) has termed this the “secondary centrifugal system.”
According to some workers, the capillaries of this system are confined to
prolongations of the neurohypophysis penetrating between the endocrine
cells (Follenius and Porte, 1962; Jasinski, 1961; Bhargava, 1966). In contrast, in the eel, according to Knowles and Vollrath (1966a,b), these
capillaries lie within a series of intervascular spaces or channels into
which the neurosecretory fibers discharge and against which the endocrine cells lie, in both the pars intermedia and pars distalis (Fig. 23).
Whatever the details, the vessels of the secondary centrifugal system
obviously come into intimate association with the adenohypophysial cells
and are the only source of blood for these cells.
In salmon and eel (Olivereau, 1954) and in Hippocamps (Boisseau,
1967) the size and number of capillaries in the adenohypophysis vanes
with age and physiological state, suggesting the possibility of a hemodynamic control of secretory activity.
From the adenohypophysial capillaries, blood is usually collected into
a superficial plexus on the outer surface of the gland, and this superficial
network of vessels drains posteriorly by a few veins which empty into the
systemic venous system via the hypocranial or hypophysial veins (Jasinski,
1961,1962; Follenius, 1965a,b; Bhargava, 1966; Fig. 24).
It will be seen that this modern work indicates a centrifugal flow of
blood from the primary longitudinal plexus in the neurohypophysis, contrary to the scheme proposed by Bretschnieder and de Wit (1947). Thus
far, there seems to be a fair measure of uniformity among teleosts studied;
J. N. BALL AND BRIDGET I. BAKER
most striking characteristic of the blood supply to the gland is that the
blood reaching the adenohypophysis has passed through capillaries in the
neurohypophysis; and further, there is no independent venous drainage
of the neurohypophysis apart perhaps from a posterior connection to the
hypophysial vein in some species (Follenius and Porte, 1962). In these
respects, the vascularization of the fish gland differs greatly from the
tetrapod condition (Wingstrand, 1959, 1966a; Green and Maxwell, 1959;
Green, 1W6).
Most students of the subject have described a collection of capillaries in the neurohypophysis, forming a vascular plexus in the neurohypophysial core, close to the adenohypophysial boundary ( e.g., cyprinodonts, Follenius, 1963a,b), or actually at the neuro-adeno interface
( several species, Jasinski, 1961, 1962). This plexus in the neurohypophysis
is the primary longitudinal plexus or system of Follenius (1965a,b; Fig.
24). In the adult Phoxinus, and no doubt in other species, it includes a
large central longitudinal sinus ( Bhargava, 1966). From this plexus a
series of capillaries passes into the adenohypophysis and forms an
elaborate network of capillaries and sinuses between the endocrine cells;
Follenius ( 1965a,b ) has termed this the “secondary centrifugal system.”
According to some workers, the capillaries of this system are confined to
prolongations of the neurohypophysis penetrating between the endocrine
cells (Follenius and Porte, 1962; Jasinski, 1961; Bhargava, 1966). In contrast, in the eel, according to Knowles and Vollrath (1966a,b), these
capillaries lie within a series of intervascular spaces or channels into
which the neurosecretory fibers discharge and against which the endocrine cells lie, in both the pars intermedia and pars distalis (Fig. 23).
Whatever the details, the vessels of the secondary centrifugal system
obviously come into intimate association with the adenohypophysial cells
and are the only source of blood for these cells.
In salmon and eel (Olivereau, 1954) and in Hippocamps (Boisseau,
1967) the size and number of capillaries in the adenohypophysis vanes
with age and physiological state, suggesting the possibility of a hemodynamic control of secretory activity.
From the adenohypophysial capillaries, blood is usually collected into
a superficial plexus on the outer surface of the gland, and this superficial
network of vessels drains posteriorly by a few veins which empty into the
systemic venous system via the hypocranial or hypophysial veins (Jasinski,
1961,1962; Follenius, 1965a,b; Bhargava, 1966; Fig. 24).
It will be seen that this modern work indicates a centrifugal flow of
blood from the primary longitudinal plexus in the neurohypophysis, contrary to the scheme proposed by Bretschnieder and de Wit (1947). Thus
far, there seems to be a fair measure of uniformity among teleosts studied;