162
A. M. PEXKS
the axons themselves. In some species, such as Salmo irideus, similar
neurosecretory elementary vesicles have been seen in the nearby nucleus
lateralis tuberis. This nucleus, which is close to the preoptico-hypophysial
tract, and which is sometimes penetrated by it, also connects to the pituitary. It shows marked seasonal activity. However, its vesicles are smaller
and have different staining properties from those of the preoptic nucleus;
the two types of vesicle are almost certainly biologically dissimilar
( Salvelinus fontinulis, Billenstien, 1962) ; Salmo irideus, Follenius, 1962).
Although the main preoptico-hypophysial tract is often rich in neurosecretory granules in its more caudal regions (carp, sazan; Polenov,
l W ) , Leatherland et al. ( 1966) and Leatherland (1967) have observed
that the tract of the eel, Anguilla anguilla, shows a small caudal accumulation of neurosecretion, which is followed by a short empty area. This
area, which was termed the “subterminal area,” lies above the anterior
margin of the adenohypophysis, and it may represent the terminations of
certain neurosecretory axons (Fig. 9 ) . It was not possible to relate any
nerve terminations to blood vessels, but it is known that a small number of
capillaries unite the vascular network of the brain with the pituitary in
this species (Jasinski, 1961 ) . However, these capillaries may connect to
the pars nervosa. Similar scanty capillary connections between the brain
and the pituitary have been noted in Lucioperca lucwperca and in Salvelinus fontina2is (Jasinski, 1962; Hill and Henderson, 1968), and it may
be pointed out that even rare capillary connections could be important if
their transmitter materials were present in high local concentrations and
if they were precisely directed. However, it is only in Phoxinus phoxinus
that there has been any claim to demonstrate definite portal vessels, with
Gomori-positive granules associated with their hypothalamic capillary
network (Barrington, 1960). In contrast, several groups of workers have
felt that the teleosts lack a conventional pituitary portal system (Green,
1951; Follenius, 1961, 1965; Sathyanesan and Chavin, 1967). Henderson’s
recent studies (1969) of the vascular supply of the pituitary of Saluelinus
fontinalis have emphasized the possibility that in teleosts the portal vessels are replaced by a capillary network which is completely internal to
the pituitary. This capillary bed joins the rostra1 region of the pars nervosa directly to the adenohypophysis, and although it is anatomically different from a classic portal system, it may well be its functional equivalent. It can only be concluded that the conventional pituitary portal
system of the teleosts is at least anatomically underdeveloped and that it
may even be absent. In connection with these problems, it is interesting
to note that Sathyanesan (1965b) has shown that hypophysectomy of
Porichthys notatus resulted in the development of a new relationship between the cut stump of the infundibulum and the local blood vessels.
This was accompanied by an accumulation of neurosecretory material at
A. M. PEXKS
the axons themselves. In some species, such as Salmo irideus, similar
neurosecretory elementary vesicles have been seen in the nearby nucleus
lateralis tuberis. This nucleus, which is close to the preoptico-hypophysial
tract, and which is sometimes penetrated by it, also connects to the pituitary. It shows marked seasonal activity. However, its vesicles are smaller
and have different staining properties from those of the preoptic nucleus;
the two types of vesicle are almost certainly biologically dissimilar
( Salvelinus fontinulis, Billenstien, 1962) ; Salmo irideus, Follenius, 1962).
Although the main preoptico-hypophysial tract is often rich in neurosecretory granules in its more caudal regions (carp, sazan; Polenov,
l W ) , Leatherland et al. ( 1966) and Leatherland (1967) have observed
that the tract of the eel, Anguilla anguilla, shows a small caudal accumulation of neurosecretion, which is followed by a short empty area. This
area, which was termed the “subterminal area,” lies above the anterior
margin of the adenohypophysis, and it may represent the terminations of
certain neurosecretory axons (Fig. 9 ) . It was not possible to relate any
nerve terminations to blood vessels, but it is known that a small number of
capillaries unite the vascular network of the brain with the pituitary in
this species (Jasinski, 1961 ) . However, these capillaries may connect to
the pars nervosa. Similar scanty capillary connections between the brain
and the pituitary have been noted in Lucioperca lucwperca and in Salvelinus fontina2is (Jasinski, 1962; Hill and Henderson, 1968), and it may
be pointed out that even rare capillary connections could be important if
their transmitter materials were present in high local concentrations and
if they were precisely directed. However, it is only in Phoxinus phoxinus
that there has been any claim to demonstrate definite portal vessels, with
Gomori-positive granules associated with their hypothalamic capillary
network (Barrington, 1960). In contrast, several groups of workers have
felt that the teleosts lack a conventional pituitary portal system (Green,
1951; Follenius, 1961, 1965; Sathyanesan and Chavin, 1967). Henderson’s
recent studies (1969) of the vascular supply of the pituitary of Saluelinus
fontinalis have emphasized the possibility that in teleosts the portal vessels are replaced by a capillary network which is completely internal to
the pituitary. This capillary bed joins the rostra1 region of the pars nervosa directly to the adenohypophysis, and although it is anatomically different from a classic portal system, it may well be its functional equivalent. It can only be concluded that the conventional pituitary portal
system of the teleosts is at least anatomically underdeveloped and that it
may even be absent. In connection with these problems, it is interesting
to note that Sathyanesan (1965b) has shown that hypophysectomy of
Porichthys notatus resulted in the development of a new relationship between the cut stump of the infundibulum and the local blood vessels.
This was accompanied by an accumulation of neurosecretory material at