8
J. N. BALL AND BRIDGET I. BAKER
2. THE MOLLY, Poecilia latipinnu AND P . fomosa
The pituitary gland of this small viviparous cyprinodont is being studied experimentally, and a general account of the gland has been published (Olivereau and Ball, 1964). The molly pituitary resembles that of
the eel, although it is proportionately shorter and deeper (Fig. 2). The
rostral pars distalis contains only two cell types, a mass of (prolactin)
cells, showing no trace of the follicular arrangement seen in the eel, and a
posterior border of e ( ACTH) cells. In contrast to the eel, the 6 (TSH)
cells occur in the proximal pars distalis, in a dorsal zone where they lie
intimately mixed with a cells. Below is a ventral zone of gonadotrops. The
pars intermedia is not penetrated by the neurohypophysis so deeply as in
the eel and contains two cell types corresponding to those of the eel.
3. OTHER TELEOSTS
Departures from the general morphology and cell distribution seen in
the above-mentioned two basic species occur, the most obvious being the
wide variations in shape and proportions of the gland. A common type
has a much shorter antero-posterior axis, and is much deeper dorsoventrally (e.g., cyprinids and salmonids) , In such cases, the gland in the
juvenile fish may resemble in general that of the eel or Poecilia, its shape
and proportions changing as the fish grows larger (Salmo, Olivereau,
1954; Mugil, Olivereau, 1968). In these deeper glands, the neurohypophysial core commonly forms an elongated central axis with the three
regions of the adenohypophysis arranged around this axis, the pars intermedia ventral below the hoop of the proximal pars distalis with the rostral
pars distalis embracing the neurohypophysial core anteriorly (see
Olivereau, 1968, Fig. 1; van Overbeeke and McBride, 1967). In these
cases, the extensive ramification of the ventral neurohypophysial core
into the pars intermedia is very elaborate.
One of the most important variables in the teleostean gland is the
location of the 6 (TSH) cells, which may lie in the proximal pars distalis,
as in Poecilia (e.g., Astyanax, Cuecobarbus, Phoxinus, and cyprinodonts),
or may be rostrally placed, as in Anguillu (e.g., clupeoids and cyprinids);
or the cells may lie in an intermediate position between the two regions
(e.g., cichlids, salmonids, and Mugil), this being one of the reasons for
uniting the rostral and proximal regions as a single pars distalis. Again,
the position of the gonadotrops is variable, being usually in the proximal
pars distalis as in Poecilia and the eel, but in the trout found in both
rostral (few) and proximal regions; and some gonadotrops invade the
rostral region even in the eel at full sexual maturity. Another variation
concerns the general structure of the rostral pars distalis. In the more
J. N. BALL AND BRIDGET I. BAKER
2. THE MOLLY, Poecilia latipinnu AND P . fomosa
The pituitary gland of this small viviparous cyprinodont is being studied experimentally, and a general account of the gland has been published (Olivereau and Ball, 1964). The molly pituitary resembles that of
the eel, although it is proportionately shorter and deeper (Fig. 2). The
rostral pars distalis contains only two cell types, a mass of (prolactin)
cells, showing no trace of the follicular arrangement seen in the eel, and a
posterior border of e ( ACTH) cells. In contrast to the eel, the 6 (TSH)
cells occur in the proximal pars distalis, in a dorsal zone where they lie
intimately mixed with a cells. Below is a ventral zone of gonadotrops. The
pars intermedia is not penetrated by the neurohypophysis so deeply as in
the eel and contains two cell types corresponding to those of the eel.
3. OTHER TELEOSTS
Departures from the general morphology and cell distribution seen in
the above-mentioned two basic species occur, the most obvious being the
wide variations in shape and proportions of the gland. A common type
has a much shorter antero-posterior axis, and is much deeper dorsoventrally (e.g., cyprinids and salmonids) , In such cases, the gland in the
juvenile fish may resemble in general that of the eel or Poecilia, its shape
and proportions changing as the fish grows larger (Salmo, Olivereau,
1954; Mugil, Olivereau, 1968). In these deeper glands, the neurohypophysial core commonly forms an elongated central axis with the three
regions of the adenohypophysis arranged around this axis, the pars intermedia ventral below the hoop of the proximal pars distalis with the rostral
pars distalis embracing the neurohypophysial core anteriorly (see
Olivereau, 1968, Fig. 1; van Overbeeke and McBride, 1967). In these
cases, the extensive ramification of the ventral neurohypophysial core
into the pars intermedia is very elaborate.
One of the most important variables in the teleostean gland is the
location of the 6 (TSH) cells, which may lie in the proximal pars distalis,
as in Poecilia (e.g., Astyanax, Cuecobarbus, Phoxinus, and cyprinodonts),
or may be rostrally placed, as in Anguillu (e.g., clupeoids and cyprinids);
or the cells may lie in an intermediate position between the two regions
(e.g., cichlids, salmonids, and Mugil), this being one of the reasons for
uniting the rostral and proximal regions as a single pars distalis. Again,
the position of the gonadotrops is variable, being usually in the proximal
pars distalis as in Poecilia and the eel, but in the trout found in both
rostral (few) and proximal regions; and some gonadotrops invade the
rostral region even in the eel at full sexual maturity. Another variation
concerns the general structure of the rostral pars distalis. In the more