1. THE PITUITARY GLAND
91
Changes in the acidophils have been described, but are impossible to
interpret (Riihle and Sterba, 1966). The basophils are PAS + ve and
A F + ve, and they are not numerous. They have been described as most
active during metamorphosis or in the spawning migration and as reduced
in activity after spawning (van de Kamer and Schreurs, 1959; RGhle and
Sterba, 1966). Roth (1957) and Evennett (1963) observed that these
PAS + ve cells in the proximal pars distalis became increasingly chromophilic during the gonadal maturation, a change that could be prevented
by gonadectomy ( Evennett, 1963). Since partial hypophysectomy indicated that gonadotropic function located in the proximal pars distalis,
Evennett (1963) concluded that these PAS + ve cells are gonadotrops.
On the other hand, Larsen (1965), working on the same species as Evennett (L. fluuiatilis), found that both the rostral and the proximal regions
secreted gonadotropins; thus, the basophils in both regions could be
gonadotrops. The changes described in the rostral basophils would fit
this idea (see above), although their activation during metamorphosis
(van de Kamer and Schreurs, 1959) could indicate a thyrotropic function, the thyroid developing at this time from the larval endostyle. At the
ultrastructural level, BAge (1967) differentiated three types of chromophils as well as chromophobes in the proximal region.
The pars intermedia has been shown to secrete MSH (Young, 1935;
Lanzing, 1954; Larsen, 1965). There is no significant penetration of this
region by the neurohypophysis. Many of the intermedia cells are chromophobic, but some authors have recognized a single chromophil, PAS + ve
and azocarmine +ve (i.e., amphiphilic) (van de Kamer and Schreurs,
1959). Others have described two chromophils: one AF + ve and
PAS - ve and elongated toward the neurohypophysis although situated
ventrally, the other A F + ve and PAS + ve and situated close to the
neurohypophysis ( Uztan and Gorbman, 1960; Riihle and Sterba, 1966).
Little certain information is available about functional changes in these
cells, although they have been examined in lamprey larvae made pale by
constant illumination, but with no clear results (Oztan and Gorbman,
1960). Various other changes have been described in the pars intermedia
in relation to metamorphosis, migration, and spawning, but they are difEcult to interpret (van der Kamer and Schreurs, 1959; &tan and Gorbman, 1960; Riihle and Sterba, 1966).
The neurohypophysis of myxinoids is peculiar, consisting of a dorsoventrally flattened hollow sac above the pars intermedia region, which
communicates with the third ventricle only by a narrow aperture (Gorbman, 196513; Wingstrand, 1966a). Nearly all the neurosecretory fibers
from the NPO terminate in the highly vascular dorsal wall of this sac,
there being few nerves or blood vessels in the ventral wall. Many of the
91
Changes in the acidophils have been described, but are impossible to
interpret (Riihle and Sterba, 1966). The basophils are PAS + ve and
A F + ve, and they are not numerous. They have been described as most
active during metamorphosis or in the spawning migration and as reduced
in activity after spawning (van de Kamer and Schreurs, 1959; RGhle and
Sterba, 1966). Roth (1957) and Evennett (1963) observed that these
PAS + ve cells in the proximal pars distalis became increasingly chromophilic during the gonadal maturation, a change that could be prevented
by gonadectomy ( Evennett, 1963). Since partial hypophysectomy indicated that gonadotropic function located in the proximal pars distalis,
Evennett (1963) concluded that these PAS + ve cells are gonadotrops.
On the other hand, Larsen (1965), working on the same species as Evennett (L. fluuiatilis), found that both the rostral and the proximal regions
secreted gonadotropins; thus, the basophils in both regions could be
gonadotrops. The changes described in the rostral basophils would fit
this idea (see above), although their activation during metamorphosis
(van de Kamer and Schreurs, 1959) could indicate a thyrotropic function, the thyroid developing at this time from the larval endostyle. At the
ultrastructural level, BAge (1967) differentiated three types of chromophils as well as chromophobes in the proximal region.
The pars intermedia has been shown to secrete MSH (Young, 1935;
Lanzing, 1954; Larsen, 1965). There is no significant penetration of this
region by the neurohypophysis. Many of the intermedia cells are chromophobic, but some authors have recognized a single chromophil, PAS + ve
and azocarmine +ve (i.e., amphiphilic) (van de Kamer and Schreurs,
1959). Others have described two chromophils: one AF + ve and
PAS - ve and elongated toward the neurohypophysis although situated
ventrally, the other A F + ve and PAS + ve and situated close to the
neurohypophysis ( Uztan and Gorbman, 1960; Riihle and Sterba, 1966).
Little certain information is available about functional changes in these
cells, although they have been examined in lamprey larvae made pale by
constant illumination, but with no clear results (Oztan and Gorbman,
1960). Various other changes have been described in the pars intermedia
in relation to metamorphosis, migration, and spawning, but they are difEcult to interpret (van der Kamer and Schreurs, 1959; &tan and Gorbman, 1960; Riihle and Sterba, 1966).
The neurohypophysis of myxinoids is peculiar, consisting of a dorsoventrally flattened hollow sac above the pars intermedia region, which
communicates with the third ventricle only by a narrow aperture (Gorbman, 196513; Wingstrand, 1966a). Nearly all the neurosecretory fibers
from the NPO terminate in the highly vascular dorsal wall of this sac,
there being few nerves or blood vessels in the ventral wall. Many of the