52
J. N. BALL AND BRlDGET I. BAKER
been variously described as chromophobic (most often), acidophilic, or
weakly basophilic.
Instrusive islets of the amphiphilic PAS + ve cells occur in the pars
distalis of Poecilia Zutipinna and P. ~ O T ~ O S U
particularly in the rostral
region (Fig. 3). The number of such islets increases with age. Similar
islets of PAS + ve cells, presumably pars intermedia cells, are found in
the rostral pars distalis of other cyprinodonts (Follenius, 196%). The
PbH+ve cells have not been found outside the pars intermedia in
Poecilia.
Pars intermedia histochemistry has been neglected. The PAS + ve
cells of Poecilia sphenops incorporate 35S04Na, rapidly ( Deminatti,
1964b), and in Mugil their granules are precipitated by a much lower
concentration of trichloroacetic acid (0.5%) than the granules of any other
cell type in the gland ( Leray, 1!366).
Acidophilic droplets, apparently colloidal, often occur between the
pars intermedia cells. Similar material in the pars intermedia of other
vertebrates has often been interpreted as an accumulation of hormonal
material (Itturiza, 1964; Itturiza and Koch, 1964; Nayar and Pandalai,
1963) or as the products of cellular degeneration (Etkin, 1967).
Few ultrastructural studies have been made on this region. The presence of two distinct cell types is confirmed in most studies, and in
AnguiZZu a third cell type has been reported (Knowles and Vollrath,
1966a), but it is not clear what this corresponds to in light microscope
studies. With the electron microscope, the two main cell types are most
readily distinguished by differences in size of their osmiophilic secretory
granules, although mitochondria1 size and details of the endoplasmic
reticulum are other criteria. Granule size and shape differ in different
species and do not correlate with granule staining reactions. Thus, in
Zoarces the PAS + ve cells have smaller granules (16&200 mp) than the
PbH cells (up to 400 mp), and the same is true of the eel ( 180 mp vs.
320 mp) (Oztan, 1966a; Knowles and Vollrath, 1966a). In contrast, in
Hippocampus the PAS + ve cells have the larger granules (250300 mp
vs. 200 mp) (Vollrath, 1967). However, as in pars distalis cells, the
granule size may vary under different conditions even within one cell
type; for example, in the elver of Anguilla the average granule size is
smaller in both cell types than in the older freshwater eel (Vollrath,
1966). The significance of these differences is unknown.
Follenius ( 1963a, 1965a), on the basis of his ultrastructural observations on the guppy, Perca and Salmo, considers that the two cell types of
the pars intermedia are not distinct, but probably represent different
stages in the functional cycle of a single cell type, an interpretation at
J. N. BALL AND BRlDGET I. BAKER
been variously described as chromophobic (most often), acidophilic, or
weakly basophilic.
Instrusive islets of the amphiphilic PAS + ve cells occur in the pars
distalis of Poecilia Zutipinna and P. ~ O T ~ O S U
particularly in the rostral
region (Fig. 3). The number of such islets increases with age. Similar
islets of PAS + ve cells, presumably pars intermedia cells, are found in
the rostral pars distalis of other cyprinodonts (Follenius, 196%). The
PbH+ve cells have not been found outside the pars intermedia in
Poecilia.
Pars intermedia histochemistry has been neglected. The PAS + ve
cells of Poecilia sphenops incorporate 35S04Na, rapidly ( Deminatti,
1964b), and in Mugil their granules are precipitated by a much lower
concentration of trichloroacetic acid (0.5%) than the granules of any other
cell type in the gland ( Leray, 1!366).
Acidophilic droplets, apparently colloidal, often occur between the
pars intermedia cells. Similar material in the pars intermedia of other
vertebrates has often been interpreted as an accumulation of hormonal
material (Itturiza, 1964; Itturiza and Koch, 1964; Nayar and Pandalai,
1963) or as the products of cellular degeneration (Etkin, 1967).
Few ultrastructural studies have been made on this region. The presence of two distinct cell types is confirmed in most studies, and in
AnguiZZu a third cell type has been reported (Knowles and Vollrath,
1966a), but it is not clear what this corresponds to in light microscope
studies. With the electron microscope, the two main cell types are most
readily distinguished by differences in size of their osmiophilic secretory
granules, although mitochondria1 size and details of the endoplasmic
reticulum are other criteria. Granule size and shape differ in different
species and do not correlate with granule staining reactions. Thus, in
Zoarces the PAS + ve cells have smaller granules (16&200 mp) than the
PbH cells (up to 400 mp), and the same is true of the eel ( 180 mp vs.
320 mp) (Oztan, 1966a; Knowles and Vollrath, 1966a). In contrast, in
Hippocampus the PAS + ve cells have the larger granules (250300 mp
vs. 200 mp) (Vollrath, 1967). However, as in pars distalis cells, the
granule size may vary under different conditions even within one cell
type; for example, in the elver of Anguilla the average granule size is
smaller in both cell types than in the older freshwater eel (Vollrath,
1966). The significance of these differences is unknown.
Follenius ( 1963a, 1965a), on the basis of his ultrastructural observations on the guppy, Perca and Salmo, considers that the two cell types of
the pars intermedia are not distinct, but probably represent different
stages in the functional cycle of a single cell type, an interpretation at