1. THE PITUITARY GLAND
85
gests secrete ACTH. Some of these possibly correspond to the Italian
workers’ .(y cells, which they suggested might secrete growth hormone,
and some of their 6 cells, which they thought might produce prolactin.
In the ventral lobe, there is more agreement about attribution of
functions. Mellinger describes PAS + ve, A F + ve, and AB + ve cells
in this lobe, which he divides on the size of their granules into V cells
(gonadotrops) and X cells (thyrotrops); the Italian workers described
here a single basophil which they thought secreted FSH.
In the chimaeroid, Hydrolagus, there are in the head of the dorsal
lobe acidophils, A F + ve cells and chromophobes, while the tail of this
region contains acidophils, basophils, and chromophobes. The putative
ventral lobe displays small cells containing PAS + ve granules, an AF +
ve cell type, also with PAS + ve granules, and chromophobes (Sathyanesan, 1965b; Jasinski and Gorbman, 1966).
While the functional identity of the various elasmobranch cells is far
from established, taking the physiological localizations of functions together with the histological data, it is clear that in the sharks and rays the
dorsal and ventral lobes, taken together, do indeed have the functions of
the pars distalis, as suggested in the nomenclature we have adopted. Alternative schemes, in which the dorsal lobe is termed the “anterior lobe”
(Mellinger, 1962b, 1966) or the “rostral and proximal pars distalis”
(deRoos and deRoos, 1967; Sathyanesan, 1965b), or simply “rostral lobe”
(Dodd et al., 1960) all imply in one way or another potentially misleading comparisons with parts of the gland in tetrapods and teleosts.
The pars intermedia lies below the thin neurohypophysial layer and
is penetrated by neurohypophysial fibers to a variable extent, forming
a neurointermedia lobe. The intermedia cells may be arranged in distinct
lobules separated by highly vascular connective tissue, or the cell cords
may fuse to form a mass of cells with an irregular plexus of blood vessels
( Meurling, 1962). The penetration of nerve fibers between the intermedia
endocrine cells may be slight as in Squalus and Etmopterus (Meurling,
1963) or very extensive as in Scylliorhinus Torpedo, and Raia (Della
Corte and Chieffi, 1962; Knowles, 1965; Chevins, 1968). Most workers
agree that only one cell type occurs in the pars intermedia, weakly PAS +
ve and acidophilic (Mellinger, 1962b; Meurling, 1963; Jasinski and
Gorbman, 1966). Knowles ( 1965) differentiated peripheral and central
cells, on the basis of shape and ultrastructure, in Scylliorhinus, and suggested they may have different functions. In the peripheral cells, he
distinguished a synthetic region at the apex of the cell and a hormone
release region at the opposite pole close to a blood vessel. Knowles (1965)
described Type A neurosecretory fibers from the NPO terminating on the
synthetic pole of the peripheral cells, and Type B fibers, possibly from the
85
gests secrete ACTH. Some of these possibly correspond to the Italian
workers’ .(y cells, which they suggested might secrete growth hormone,
and some of their 6 cells, which they thought might produce prolactin.
In the ventral lobe, there is more agreement about attribution of
functions. Mellinger describes PAS + ve, A F + ve, and AB + ve cells
in this lobe, which he divides on the size of their granules into V cells
(gonadotrops) and X cells (thyrotrops); the Italian workers described
here a single basophil which they thought secreted FSH.
In the chimaeroid, Hydrolagus, there are in the head of the dorsal
lobe acidophils, A F + ve cells and chromophobes, while the tail of this
region contains acidophils, basophils, and chromophobes. The putative
ventral lobe displays small cells containing PAS + ve granules, an AF +
ve cell type, also with PAS + ve granules, and chromophobes (Sathyanesan, 1965b; Jasinski and Gorbman, 1966).
While the functional identity of the various elasmobranch cells is far
from established, taking the physiological localizations of functions together with the histological data, it is clear that in the sharks and rays the
dorsal and ventral lobes, taken together, do indeed have the functions of
the pars distalis, as suggested in the nomenclature we have adopted. Alternative schemes, in which the dorsal lobe is termed the “anterior lobe”
(Mellinger, 1962b, 1966) or the “rostral and proximal pars distalis”
(deRoos and deRoos, 1967; Sathyanesan, 1965b), or simply “rostral lobe”
(Dodd et al., 1960) all imply in one way or another potentially misleading comparisons with parts of the gland in tetrapods and teleosts.
The pars intermedia lies below the thin neurohypophysial layer and
is penetrated by neurohypophysial fibers to a variable extent, forming
a neurointermedia lobe. The intermedia cells may be arranged in distinct
lobules separated by highly vascular connective tissue, or the cell cords
may fuse to form a mass of cells with an irregular plexus of blood vessels
( Meurling, 1962). The penetration of nerve fibers between the intermedia
endocrine cells may be slight as in Squalus and Etmopterus (Meurling,
1963) or very extensive as in Scylliorhinus Torpedo, and Raia (Della
Corte and Chieffi, 1962; Knowles, 1965; Chevins, 1968). Most workers
agree that only one cell type occurs in the pars intermedia, weakly PAS +
ve and acidophilic (Mellinger, 1962b; Meurling, 1963; Jasinski and
Gorbman, 1966). Knowles ( 1965) differentiated peripheral and central
cells, on the basis of shape and ultrastructure, in Scylliorhinus, and suggested they may have different functions. In the peripheral cells, he
distinguished a synthetic region at the apex of the cell and a hormone
release region at the opposite pole close to a blood vessel. Knowles (1965)
described Type A neurosecretory fibers from the NPO terminating on the
synthetic pole of the peripheral cells, and Type B fibers, possibly from the