2. THE NEUROHYPOPHYSIS
153
and Chavin (1967) has shown that it has clear similarities to that of the
other preteleost groups. The following general account is based on the
results of these authors, except where otherwise indicated.
The neurohypophysial system is well developed in the various species
of bowfin, Amia, and of garpike, Lepidosteus (Green, 1951). The preoptic nucleus is relatively short ( Amia calua, Lepidosteus osseus; Charlton, 1932). In Lepidosteus osseus and L. platostomus it lies antero-dorsal
to the optic chiasma, on both sides of the preoptic recess, and in a
position similar to that of the teleost fish (Charlton, 1932; Sathyanesan
and Chavin, 1967; see Fig. 8 ) . However, in Amiu calva, the preoptic
nucleus is dorsal to the pituitary; this is because the gland is drawn forward rostrally in a remarkable manner, so that it lies beneath the optic
chiasma (Sathyanesan and Chavin, 1967). In Amiu calua, the preoptic
nucleus closely resembles that of the teleosts in being divided into a
ventral region of small cells and a dorsal region of large neurons. However, in species of Lepidosteus, the distinction is less clear, since some
large cells of the dorsal group intrude among the smaller variety, in a
manner which is reminiscent of the sturgeon, Acipenser fulvescens
( Sathyanesan and Chavin, 1967). The preoptic cells contain variable
amounts of aldehyde-fuchsin-positive neurosecretion. The well-marked
preoptico-hypophysial tract which leaves the nucleus can be resolved
into a number of groups of fibers, which pass caudally along the infundibular floor ( Amiu calva, Lepidosteus osseus; Green, 1951 ). These
Fig. 8. The hypothalamus and pituitary of the garpike, Lepidosteus osseus, sagittal section. Note that the processes of the pars nervosa invade only the caudal
region = pars intermedia. (ON) optic chiasma, ( NPO) preoptic nucleus, ( NLT)
nucleus lateralis tuberis, (INR) infundibular cavity, ( N H ) pars nervosa, (PI ) pars
intermedia, (PD) pars distalis of adenohypophysis, and (SV) saccus vasculosus.
From A. G. Sathyanesan and W. Chavin: Hypothalamo-hypophyseal neurosecretory
system in the primitive actinopterygian fishes (Holostei and Chondrostei). Acta Anat.
68, 284-299 (Karger, Basel/New York 1967).
153
and Chavin (1967) has shown that it has clear similarities to that of the
other preteleost groups. The following general account is based on the
results of these authors, except where otherwise indicated.
The neurohypophysial system is well developed in the various species
of bowfin, Amia, and of garpike, Lepidosteus (Green, 1951). The preoptic nucleus is relatively short ( Amia calua, Lepidosteus osseus; Charlton, 1932). In Lepidosteus osseus and L. platostomus it lies antero-dorsal
to the optic chiasma, on both sides of the preoptic recess, and in a
position similar to that of the teleost fish (Charlton, 1932; Sathyanesan
and Chavin, 1967; see Fig. 8 ) . However, in Amiu calva, the preoptic
nucleus is dorsal to the pituitary; this is because the gland is drawn forward rostrally in a remarkable manner, so that it lies beneath the optic
chiasma (Sathyanesan and Chavin, 1967). In Amiu calua, the preoptic
nucleus closely resembles that of the teleosts in being divided into a
ventral region of small cells and a dorsal region of large neurons. However, in species of Lepidosteus, the distinction is less clear, since some
large cells of the dorsal group intrude among the smaller variety, in a
manner which is reminiscent of the sturgeon, Acipenser fulvescens
( Sathyanesan and Chavin, 1967). The preoptic cells contain variable
amounts of aldehyde-fuchsin-positive neurosecretion. The well-marked
preoptico-hypophysial tract which leaves the nucleus can be resolved
into a number of groups of fibers, which pass caudally along the infundibular floor ( Amiu calva, Lepidosteus osseus; Green, 1951 ). These
Fig. 8. The hypothalamus and pituitary of the garpike, Lepidosteus osseus, sagittal section. Note that the processes of the pars nervosa invade only the caudal
region = pars intermedia. (ON) optic chiasma, ( NPO) preoptic nucleus, ( NLT)
nucleus lateralis tuberis, (INR) infundibular cavity, ( N H ) pars nervosa, (PI ) pars
intermedia, (PD) pars distalis of adenohypophysis, and (SV) saccus vasculosus.
From A. G. Sathyanesan and W. Chavin: Hypothalamo-hypophyseal neurosecretory
system in the primitive actinopterygian fishes (Holostei and Chondrostei). Acta Anat.
68, 284-299 (Karger, Basel/New York 1967).