180
A. M. PERKS
appears to be a tendency for them to be divided into different tracts. In
Protopterus aethiopicus, the preoptico-hypophysial tract which enters the
infundibulum is notably diffuse, but its clearest component curves laterally
through the walls of the infundibular process, on both sides (Kerr and
van Oordt, 1966). It subdivides into upper and lower tracts in a manner
reminiscent of preteleost species such as Polyptew senegalis, and the
sturgeon, Acipenser fulvescens (Kerr and van Oordt, 1966). Many of the
axons of the ventral tract contact a dense capillary network, which has
been seen to run in furrows within the infundibular wall, just anterior
to the rostral margin of the pituitary, in Protopterus annectens (Protopterms aethwpicus, Kerr and van Oordt, 1966; P. annectens, Wingstrand,
1966). This region of the infundibular wall is not thickened in any way,
and is not clearly demarcated from the pars nervosa (Protopterus
annectens; Wingstrand, 1966, Dodd and Kerr, 1963). However, it can be
distinguished from the neural lobe by its lower content of neurosecretion
and by the presence of the invading capillaries (Protopterus annectens;
Wingstrand, 1959a; Dodd and Kerr, 1963). The capillaries connect to
short portal vessels which pass into the rostral tip of the adenohypophysis.
It is clear that the lungfish possess a functional median eminence and
pituitary portal system ( Wingstrand, 1956, 1959a, 1966).
Although a few axons of the ventral tract carry beaded neurosecretory
droplets past the median eminence into the neural lobe, most of the
preoptico-hypophysial fibers reach the pituitary through the dorsal branch
of the tract. These dorsal axons pass through the lateral and dorsal walls
of the caudal infundibular process and form a pars nervosa at its extremity ( Protopterms aethiopicus, Kerr and van Oordt, 1966).
The pars nervosa originates as an outgrowth of neural tissue in the medial walls of the two caudally directed pockets, which are formed at the
caudal limit of the infundibulum (Protopterus sp., Wingstrand, 1966; Protopterus aethiopicus, Kerr and van Oordt, 1966). It is a large, conspicuous
structure, which lies dorsal to the pars intermedia, and was once referred
to as the “infundibular gland” (Lepidosiren sp., de Beer, 1926; Charipper,
1937; Neoceratodus forsteri, Griffiths, 1938; Protopterus annectens, Dodd
and Kerr, 1963). It is made up of a mass of ramifying rods of neural
tissue, and of intricate tubules which are penetrated by extensions from
the infundibular cavity ( Lepidosiren sp., Charipper, 1937; Neoceratodus
forsteri, Griffiths, 1938; Protopterus annectens, Wingstrand, 1956, Dodd
and Kerr, 1963; P . aethiopicus, Dawson, 1940; Kerr and van Oordt, 1966).
The tubules are lined by ependymal cells, and these cells also form a
central core to many of the solid rods of neural tissue (Neoceratodus
forsteri, Griffiths, 1938; Protopterus annectens, Dodd and Kerr, 1963;
Wingstrand, 1966; P. aethiopicus, Dawson, 1940; Kerr and van Oordt,
A. M. PERKS
appears to be a tendency for them to be divided into different tracts. In
Protopterus aethiopicus, the preoptico-hypophysial tract which enters the
infundibulum is notably diffuse, but its clearest component curves laterally
through the walls of the infundibular process, on both sides (Kerr and
van Oordt, 1966). It subdivides into upper and lower tracts in a manner
reminiscent of preteleost species such as Polyptew senegalis, and the
sturgeon, Acipenser fulvescens (Kerr and van Oordt, 1966). Many of the
axons of the ventral tract contact a dense capillary network, which has
been seen to run in furrows within the infundibular wall, just anterior
to the rostral margin of the pituitary, in Protopterus annectens (Protopterms aethwpicus, Kerr and van Oordt, 1966; P. annectens, Wingstrand,
1966). This region of the infundibular wall is not thickened in any way,
and is not clearly demarcated from the pars nervosa (Protopterus
annectens; Wingstrand, 1966, Dodd and Kerr, 1963). However, it can be
distinguished from the neural lobe by its lower content of neurosecretion
and by the presence of the invading capillaries (Protopterus annectens;
Wingstrand, 1959a; Dodd and Kerr, 1963). The capillaries connect to
short portal vessels which pass into the rostral tip of the adenohypophysis.
It is clear that the lungfish possess a functional median eminence and
pituitary portal system ( Wingstrand, 1956, 1959a, 1966).
Although a few axons of the ventral tract carry beaded neurosecretory
droplets past the median eminence into the neural lobe, most of the
preoptico-hypophysial fibers reach the pituitary through the dorsal branch
of the tract. These dorsal axons pass through the lateral and dorsal walls
of the caudal infundibular process and form a pars nervosa at its extremity ( Protopterms aethiopicus, Kerr and van Oordt, 1966).
The pars nervosa originates as an outgrowth of neural tissue in the medial walls of the two caudally directed pockets, which are formed at the
caudal limit of the infundibulum (Protopterus sp., Wingstrand, 1966; Protopterus aethiopicus, Kerr and van Oordt, 1966). It is a large, conspicuous
structure, which lies dorsal to the pars intermedia, and was once referred
to as the “infundibular gland” (Lepidosiren sp., de Beer, 1926; Charipper,
1937; Neoceratodus forsteri, Griffiths, 1938; Protopterus annectens, Dodd
and Kerr, 1963). It is made up of a mass of ramifying rods of neural
tissue, and of intricate tubules which are penetrated by extensions from
the infundibular cavity ( Lepidosiren sp., Charipper, 1937; Neoceratodus
forsteri, Griffiths, 1938; Protopterus annectens, Wingstrand, 1956, Dodd
and Kerr, 1963; P . aethiopicus, Dawson, 1940; Kerr and van Oordt, 1966).
The tubules are lined by ependymal cells, and these cells also form a
central core to many of the solid rods of neural tissue (Neoceratodus
forsteri, Griffiths, 1938; Protopterus annectens, Dodd and Kerr, 1963;
Wingstrand, 1966; P. aethiopicus, Dawson, 1940; Kerr and van Oordt,