74
J. N. BALL AND BRlDGET I. BAKER
comparable to the anterior region of the teleostean neurohypophysial
core, and to the shallow anterior part of the neurohypophysis dorsal to
the pars distalis (the infundibular floor) in the primitive bony fishes.
111. THE PITUITARY GLAND IN PRIMITIVE BONY FISHES
Bony fishes belong to the class Actinopterygii, and the vast majority
belong to the most recently evolved group of actinopterygians, the superorder Teleostei (see Fig. 2 5 ) . In addition, there are a few surviving members of the more ancient superorders Chondrostei and Holostei. The
pituitary gland in these primitive forms is of obvious interest in possibly
indicating the evolutionary developments which lead to the extreme
specializations exhibited by the teleostean gland. Unfortunately, published information is almost entirely limited to anatomical and histological descriptions, with little experimental data to help identdy the various
cell types.
A. Superorder Chondrostei
1. ORDER PALAEONISCOIDEI ( POLYPTERUS AND CALAMOICHTHYS)
General accounts of the pituitary in these fishes have been given recently by Dodd and Kerr (1963) and Wingstrand ( 1966a), and Kerr
(1968) has made a detailed histological study. The most remarkable feature is the presence in the adult of a persistent remnant of the ventral
part of Rathke’s pouch, the hypophysial duct, which opens ventrally into
the roof of the mouth and dorsally into an expanded space in the ventral
part of the pars distalis (Fig. 25E). From this space, short diverticuli
penetrate the pars distalis, forming vesicles in sections (Dodd and Kerr,
1963). Kerr (1968) equates this ventral part of the gland with the rostra1
pars distalis of teleosts, although the cells lining the vesicles and duct are
peculiar, elongated chromophobes with some basophilic secretion at their
distal apices (Kerr, 1968; Ball, 1968), unlike the acidophilic
cells
around the follicles of primitive teleosts with which the duct cells are
comparable on Kerr’s interpretation. Associated with the vesicles and
their elongated lining cells are typical basophils (Type 3 basophils),
which are PAS + ve, AB + ve (weakly), but A F + ve. Type 3 basophils
also occur in the dorsal region of the gland, which is probably equivalent
to the proximal pars distalis of teleosts. In this dorsal region, Kerr described a very small scattered acidophil, and two further basophils, most
J. N. BALL AND BRlDGET I. BAKER
comparable to the anterior region of the teleostean neurohypophysial
core, and to the shallow anterior part of the neurohypophysis dorsal to
the pars distalis (the infundibular floor) in the primitive bony fishes.
111. THE PITUITARY GLAND IN PRIMITIVE BONY FISHES
Bony fishes belong to the class Actinopterygii, and the vast majority
belong to the most recently evolved group of actinopterygians, the superorder Teleostei (see Fig. 2 5 ) . In addition, there are a few surviving members of the more ancient superorders Chondrostei and Holostei. The
pituitary gland in these primitive forms is of obvious interest in possibly
indicating the evolutionary developments which lead to the extreme
specializations exhibited by the teleostean gland. Unfortunately, published information is almost entirely limited to anatomical and histological descriptions, with little experimental data to help identdy the various
cell types.
A. Superorder Chondrostei
1. ORDER PALAEONISCOIDEI ( POLYPTERUS AND CALAMOICHTHYS)
General accounts of the pituitary in these fishes have been given recently by Dodd and Kerr (1963) and Wingstrand ( 1966a), and Kerr
(1968) has made a detailed histological study. The most remarkable feature is the presence in the adult of a persistent remnant of the ventral
part of Rathke’s pouch, the hypophysial duct, which opens ventrally into
the roof of the mouth and dorsally into an expanded space in the ventral
part of the pars distalis (Fig. 25E). From this space, short diverticuli
penetrate the pars distalis, forming vesicles in sections (Dodd and Kerr,
1963). Kerr (1968) equates this ventral part of the gland with the rostra1
pars distalis of teleosts, although the cells lining the vesicles and duct are
peculiar, elongated chromophobes with some basophilic secretion at their
distal apices (Kerr, 1968; Ball, 1968), unlike the acidophilic
cells
around the follicles of primitive teleosts with which the duct cells are
comparable on Kerr’s interpretation. Associated with the vesicles and
their elongated lining cells are typical basophils (Type 3 basophils),
which are PAS + ve, AB + ve (weakly), but A F + ve. Type 3 basophils
also occur in the dorsal region of the gland, which is probably equivalent
to the proximal pars distalis of teleosts. In this dorsal region, Kerr described a very small scattered acidophil, and two further basophils, most