1. THE PIlWITARY GLAND
9
primitive teleosts ( isospondylous forms, salmonids, clupeoids, and apodes), the prolactin cells of this region are arranged around follicles, as
in the eel. This follicular arrangement of the prolactin cells in these
primitive teleosts recalls the similar structure of this region in ganoid
fishes ( Section 111). In certain clupeoid and salmonid fry, and in the adult
Hiku ilishu, the lumina of the rostral follicles communicate with a persistent orohypophysial duct which probably represents the cavity of the
embryonic Rathke’s pouch ( Sathyanesan, 1963). In most teleosts the
orohypophysial duct is never present; or if formed it disappears in the
adult, and the rostral follicles in the pars distalis of adult isospondylous
teleosts should probably be regarded as a primitive feature, as suggested
long ago by earlier workers on the gland (e.g., de Beer, 1926; Kerr, 1949;
see Wingstrand, 1966a).
Despite these and other variations in the morphology of the gland, the
teleost pituitary when studied in detail usually presents the principal
parts described for the eel and Poeciliu, and the pars distalis can generally
be seen to present rostral and proximal regions. In certain cases the
distinctions may be less clear, and in Lepidogobius lepidus Kobayashi
et al. (1959) have described four distinct tinctorial zones in the pars
distalis. Probably the experimental analysis of this species would reveal
a functional agreement with the more usual roughly bipartite pars distalis.
Lepidogobius demonstrates further unusual features: the whole pituitary is pressed up into the hypothalamus, almost obliterating the third
ventricle, the neurosecretory fibers from the hypothalamus take an unusual course to the neurohypophysis, and the neurohypophysial core does
not penetrate deeply into the adenohypophysis, not even into the pars
intermedia ( Kobayashi et al., 1959). Another specialized arrangement is
seen in Hippocampus where the neurohypophysis extends to enclose the
pars intermedia laterally, ventrally, dorsally, and posteriorly, so that the
posterior region of the gland consists of a central core of pars intermedia
enclosed in a sleeve of neurohypophysial tissue (Da Lage, 1958).
B. Histophysiology of the Adenohypophysis
The teleostean adenohypophysis has been shown to secrete the usual
complement of hormones, prolactin, growth hormone (see chapter by
Ball, this volume), gonadobopins, TSH, ACTH, and MSH (Pickford and
Atz, 1957; Hoar, 1966; Ball et al., 1965; Ball and Olivereau, 1966; van
Overbeeke and Ahsan, 1966; Ball, 1969). Each of these factors has been
allocated by experimentation to the cell type that secretes it, and the cell
types will now be treated in turn.
9
primitive teleosts ( isospondylous forms, salmonids, clupeoids, and apodes), the prolactin cells of this region are arranged around follicles, as
in the eel. This follicular arrangement of the prolactin cells in these
primitive teleosts recalls the similar structure of this region in ganoid
fishes ( Section 111). In certain clupeoid and salmonid fry, and in the adult
Hiku ilishu, the lumina of the rostral follicles communicate with a persistent orohypophysial duct which probably represents the cavity of the
embryonic Rathke’s pouch ( Sathyanesan, 1963). In most teleosts the
orohypophysial duct is never present; or if formed it disappears in the
adult, and the rostral follicles in the pars distalis of adult isospondylous
teleosts should probably be regarded as a primitive feature, as suggested
long ago by earlier workers on the gland (e.g., de Beer, 1926; Kerr, 1949;
see Wingstrand, 1966a).
Despite these and other variations in the morphology of the gland, the
teleost pituitary when studied in detail usually presents the principal
parts described for the eel and Poeciliu, and the pars distalis can generally
be seen to present rostral and proximal regions. In certain cases the
distinctions may be less clear, and in Lepidogobius lepidus Kobayashi
et al. (1959) have described four distinct tinctorial zones in the pars
distalis. Probably the experimental analysis of this species would reveal
a functional agreement with the more usual roughly bipartite pars distalis.
Lepidogobius demonstrates further unusual features: the whole pituitary is pressed up into the hypothalamus, almost obliterating the third
ventricle, the neurosecretory fibers from the hypothalamus take an unusual course to the neurohypophysis, and the neurohypophysial core does
not penetrate deeply into the adenohypophysis, not even into the pars
intermedia ( Kobayashi et al., 1959). Another specialized arrangement is
seen in Hippocampus where the neurohypophysis extends to enclose the
pars intermedia laterally, ventrally, dorsally, and posteriorly, so that the
posterior region of the gland consists of a central core of pars intermedia
enclosed in a sleeve of neurohypophysial tissue (Da Lage, 1958).
B. Histophysiology of the Adenohypophysis
The teleostean adenohypophysis has been shown to secrete the usual
complement of hormones, prolactin, growth hormone (see chapter by
Ball, this volume), gonadobopins, TSH, ACTH, and MSH (Pickford and
Atz, 1957; Hoar, 1966; Ball et al., 1965; Ball and Olivereau, 1966; van
Overbeeke and Ahsan, 1966; Ball, 1969). Each of these factors has been
allocated by experimentation to the cell type that secretes it, and the cell
types will now be treated in turn.