1. THE PITUITARY GLAND
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laries are in close proximity to the neurosecretory fibers in the infundibular floor. It is possible that some neurovascular exchange may occur here,
as appears to be the case in holosteans (Section 111, B), capillary
branches also penetrating the pars distalis from the connective tissue
plexus.
2. ORDER ACIPENSEROIDEI ( ACIPENSER AND POLYDON)
The sturgeon pituitary has been studied many times, particularly by
Russian workers, but there is still little detailed information about its
histophysiology. The most notable anatomical feature is the persistence
of a large central hypophysial cavity or cleft, apparently a remnant of the
dorsal part of Rathke’s pouch (Kerr, 1949; Dodd and Kerr, 1963; Wingstrand, 1966a), although unlike the palaeoniscids the sturgeons do not
retain a hypophysial duct to the roof of the mouth. The hypophysial cleft
largely separates the posterior pars intermedia from the anterior pars
distalis, and also largely splits the latter into dorsal and ventral portions
( Fig. 25C). The cleft gives off numerous tubular extensions, particularly
dorsally but also anteriorly and ventrally. In addition to these tubules
there are in the anterior and ventral pars distalis closed vesicles, with no
connection to the cleft. In the absence of detailed embryological information their morphological status is uncertain, but Kerr (1949) assumes they
are derived from the cleft tubules. These vesicles are presumably homologous with the follicles of the rostral pars distalis of holosteans and
primitive teleosts. Acipenser fluvescens shows acidophils, often elongated,
oriented around these vesicles, together with equally abundant rounded
basophils and chromophobes (Kerr, 1949). However, in the rostral region of A. steZlutus, where the vesicles predominate, Barannikova (1949)
described strongly acidophilic cells around the vesicles, together with
amphiphils and only a few basophils. Both authors agree that the vesicles
usually contain basophilic colloid as in holosteans and teleosts.
The ventral pars distalis, beneath the hypophysial cleft, was considered by Kerr to be an extension of the rostral pars distalis, with the same
cellular composition, but Barannikova distinguishes this zone from the
rostral region, since its acidophil cells stain more weakly and it contains
many more basophils and small chromophobes. In the dorsal pars distalis, above the cleft, Kerr described regular columns of cells, arranged
around tubular extensions of the cleft, containing acidophils and basophils. Barannikova (1949) states that this region contains the faint acidophils, basophils, and chromophobes also found in the ventral zone, together with strongly staining acidophils. By bioassay of dissected glands
of A. stellatus, Barannikova (1949) located gonadotropin secretion in the
77
laries are in close proximity to the neurosecretory fibers in the infundibular floor. It is possible that some neurovascular exchange may occur here,
as appears to be the case in holosteans (Section 111, B), capillary
branches also penetrating the pars distalis from the connective tissue
plexus.
2. ORDER ACIPENSEROIDEI ( ACIPENSER AND POLYDON)
The sturgeon pituitary has been studied many times, particularly by
Russian workers, but there is still little detailed information about its
histophysiology. The most notable anatomical feature is the persistence
of a large central hypophysial cavity or cleft, apparently a remnant of the
dorsal part of Rathke’s pouch (Kerr, 1949; Dodd and Kerr, 1963; Wingstrand, 1966a), although unlike the palaeoniscids the sturgeons do not
retain a hypophysial duct to the roof of the mouth. The hypophysial cleft
largely separates the posterior pars intermedia from the anterior pars
distalis, and also largely splits the latter into dorsal and ventral portions
( Fig. 25C). The cleft gives off numerous tubular extensions, particularly
dorsally but also anteriorly and ventrally. In addition to these tubules
there are in the anterior and ventral pars distalis closed vesicles, with no
connection to the cleft. In the absence of detailed embryological information their morphological status is uncertain, but Kerr (1949) assumes they
are derived from the cleft tubules. These vesicles are presumably homologous with the follicles of the rostral pars distalis of holosteans and
primitive teleosts. Acipenser fluvescens shows acidophils, often elongated,
oriented around these vesicles, together with equally abundant rounded
basophils and chromophobes (Kerr, 1949). However, in the rostral region of A. steZlutus, where the vesicles predominate, Barannikova (1949)
described strongly acidophilic cells around the vesicles, together with
amphiphils and only a few basophils. Both authors agree that the vesicles
usually contain basophilic colloid as in holosteans and teleosts.
The ventral pars distalis, beneath the hypophysial cleft, was considered by Kerr to be an extension of the rostral pars distalis, with the same
cellular composition, but Barannikova distinguishes this zone from the
rostral region, since its acidophil cells stain more weakly and it contains
many more basophils and small chromophobes. In the dorsal pars distalis, above the cleft, Kerr described regular columns of cells, arranged
around tubular extensions of the cleft, containing acidophils and basophils. Barannikova (1949) states that this region contains the faint acidophils, basophils, and chromophobes also found in the ventral zone, together with strongly staining acidophils. By bioassay of dissected glands
of A. stellatus, Barannikova (1949) located gonadotropin secretion in the