88
J. N. BALL AND BRIDGET I. BAKER
There are no published accounts of induced changes in the amount
of material in the neurohypophysis of these fishes. Peptides with the usual
properties occur in the neurohypophysis of elasmobranchs, although
apparently differing from the principles in other groups (see Sawyer,
1966b, 1967). Perks and Dodd (1960) showed that after section of the
hypothalamo-neurohypophysial tract of Scylliorhinus the oxytocic activity
of the neurointermediate lobe eventually disappeared, and Chevins
(1968) found that typical A F + ve neurosecretory material eventually
disappeared from the tract and neurointermediate lobe of Raia following
ablation of the NPO.
The blood supply to the elasmobranch pituitary has attracted great
interest ( Meurling, 1960; Mellinger, 1960a,b, 1962b, 1963a, 1965;
Mellinger et al., 1962; Follenius, 1965b) and is reviewed by Meurling
( 1967a). The vascular supply in chimaeroids is described by Sathyanesan
(1965b), Jasinski and Gorbman (1966), and Meurling (196713). Apart
from the dorsal pars distalis in the chimaeroid, Hydrolagus (Jasinski and
Gorbman, 1966), it appears that each lobe of the pituitary receives
arterial blood directly from either the vertebral or internal carotid arteries. In addition, there is evidence for a hypophysial portal system,
although its details differ in different accounts. All authors agree that
there is a region in the anterior infundibular floor (anterior hypothalamus) where neurosecretory axons from the NPO (and some from the
NLT) are grouped around a capillary plexus in a way that suggests a
neurohemal organ ( Meurling, 1960; Mellinger, 1960a,b, 1963a; Chevins,
1968). Ultrastructural studies confirmed the presence in this region of
neurosecretory terminations on the capillary walls, strongly resembling
those in the mammalian median eminence (Mellinger et al., 1962;
Mellinger, 1963a). From this primary plexus in the median eminence,
most of the blood passes backward in capillaries, some of which supply
the tail of the dorsal lobe (Mellinger, 1960a,b, 1965; Meurling, 1963;
Follenius, 1965b), while a few (Mellinger) or many (Meurling, 1967a;
Chevins, 1968) pass back to supply the neurointermediate lobe. The head
of the dorsal lobe is said by some authors to receive portal blood from
the anterior part of the median eminence (Follenius, 196513; Chevins,
1968), but other workers have not described this (Mellinger, 1960a,b,
1965; Meurling, 1960, 1967a). Most workers have said that the ventral
lobe receives no blood from the portal vessels (Mellinger, 1963a; Meurling, 1967a; Follenius, 1965b), but in Raia sp. Chevins (1968) finds that
blood enters the ventral lobe from sinuses in the dorsal lobe, so that at
least some of this blood must be portal in origin.
In the chimaeroid, Hydrolagus, the portal system is similar. The dorsal lobe, however, does not receive any direct arterial blood, and numer-
J. N. BALL AND BRIDGET I. BAKER
There are no published accounts of induced changes in the amount
of material in the neurohypophysis of these fishes. Peptides with the usual
properties occur in the neurohypophysis of elasmobranchs, although
apparently differing from the principles in other groups (see Sawyer,
1966b, 1967). Perks and Dodd (1960) showed that after section of the
hypothalamo-neurohypophysial tract of Scylliorhinus the oxytocic activity
of the neurointermediate lobe eventually disappeared, and Chevins
(1968) found that typical A F + ve neurosecretory material eventually
disappeared from the tract and neurointermediate lobe of Raia following
ablation of the NPO.
The blood supply to the elasmobranch pituitary has attracted great
interest ( Meurling, 1960; Mellinger, 1960a,b, 1962b, 1963a, 1965;
Mellinger et al., 1962; Follenius, 1965b) and is reviewed by Meurling
( 1967a). The vascular supply in chimaeroids is described by Sathyanesan
(1965b), Jasinski and Gorbman (1966), and Meurling (196713). Apart
from the dorsal pars distalis in the chimaeroid, Hydrolagus (Jasinski and
Gorbman, 1966), it appears that each lobe of the pituitary receives
arterial blood directly from either the vertebral or internal carotid arteries. In addition, there is evidence for a hypophysial portal system,
although its details differ in different accounts. All authors agree that
there is a region in the anterior infundibular floor (anterior hypothalamus) where neurosecretory axons from the NPO (and some from the
NLT) are grouped around a capillary plexus in a way that suggests a
neurohemal organ ( Meurling, 1960; Mellinger, 1960a,b, 1963a; Chevins,
1968). Ultrastructural studies confirmed the presence in this region of
neurosecretory terminations on the capillary walls, strongly resembling
those in the mammalian median eminence (Mellinger et al., 1962;
Mellinger, 1963a). From this primary plexus in the median eminence,
most of the blood passes backward in capillaries, some of which supply
the tail of the dorsal lobe (Mellinger, 1960a,b, 1965; Meurling, 1963;
Follenius, 1965b), while a few (Mellinger) or many (Meurling, 1967a;
Chevins, 1968) pass back to supply the neurointermediate lobe. The head
of the dorsal lobe is said by some authors to receive portal blood from
the anterior part of the median eminence (Follenius, 196513; Chevins,
1968), but other workers have not described this (Mellinger, 1960a,b,
1965; Meurling, 1960, 1967a). Most workers have said that the ventral
lobe receives no blood from the portal vessels (Mellinger, 1963a; Meurling, 1967a; Follenius, 1965b), but in Raia sp. Chevins (1968) finds that
blood enters the ventral lobe from sinuses in the dorsal lobe, so that at
least some of this blood must be portal in origin.
In the chimaeroid, Hydrolagus, the portal system is similar. The dorsal lobe, however, does not receive any direct arterial blood, and numer-