these have not been substantiated (see for instance CHESTER JONES et al.,1965).
A fresh approach towards the problems of identifying a secretion has been made
by CHESTER JONES and eight of his collaborators (1966); extracts of the corpuscles
of STANNIUS from eels, when injected into rats, or eels, increased the blood pressure. Removal of the corpuscles from the eel reduced its blood pressure. CHESTER
JONES et al. have indicated certain similarities between this pressor material and
renin, and suggest that it may be part of a system homologous to the renin-angiotensin-aldosterone axis of tetrapods. This would account for some of the similarities between ablation of the STANNIUS corpuscles and interrenalectomy in eels,
though the effects of the two operations are not completely identical; both procedures result in a decreased plasma sodium level, but only ablation of the corpuscles
produces the elevated potassium and calcium concentrations (CHAN et al., 1967a).
Endocrine tissues usually have been found to have several roles and secretions; this
could also apply to the corpuscles of STANNIUS.
b) The Caudal Neurosecretory System and the Urophysis
Neurosecretory nerve fibres have been histologically identified in the caudal
regions of the spinal cord in a number of fishes . The literature has been reviewed
by FRIDBERG and BERN (1968). These neurons (DAHLGREN cells) were described
by SPEIDEL (1919) in chondrichthyeans. ENAMI(1955) described a discrete bundle
of such cells in the japanese eel, Anguilla japonica, where they form a distinct lobe
of neurosecretory cells abutting onto a bed of capillaries to form a neurohaemal
junction. The degree of aggregation of such cells to form a lobate-structure, the
urophysis, differs in various species, and achieves its most distinct form in certain
teleosts. In the Chondrichthyes the cells are situated in a diffuse area, which in
Raja batis, may extend over the area of the last 55 vertebrae. These caudal neurosecretory fibres have only been identified in the Chondrichthyes, releostean and
chondrostean bon y fishes.
The neurosecretory cells in the caudal regions of fish, and those of the hypothalame-neurohypophysial region of the vertebrate brain, are analogous in their general histological properties. However, the caudal cells, in contrast to the cephalic
ones, do not produce secretions that can be stained with iron-alum haematoxylin.
Both groups of neurosecretory material are thought to be protein-like. The caudal
neurosecretory neurons, like typical neurosecretory cells, can transmit nerve impulses (MORITA, ISHIBASHI, and YAMASHITA, 1961).
An endocrine role for the caudal neurosecretory cells remains to be established.
Their possible role in osmoregulation has been explored, probably partly as a result
of their morphological analogies with the neurohypophysis. Extirpation of the
urophysis in some teleosts has failed to reveal evidence for such a function, but
the potential regeneration of such tissues makes such available evidence inconclusive (FRIDBERG and BERN, 1968). MAETZ, BOURGUET, and LAHLOUH (1963)
found that when extracts of the urophysis were reinjected into the goldfish, Carassiusauratus, there was an increased branchial uptake of sodium and an increased
urine flow, with a reduced renal loss of sodium. These experiments need extending
to other species of fish before any general conclusions can be drawn, but at the
79
A fresh approach towards the problems of identifying a secretion has been made
by CHESTER JONES and eight of his collaborators (1966); extracts of the corpuscles
of STANNIUS from eels, when injected into rats, or eels, increased the blood pressure. Removal of the corpuscles from the eel reduced its blood pressure. CHESTER
JONES et al. have indicated certain similarities between this pressor material and
renin, and suggest that it may be part of a system homologous to the renin-angiotensin-aldosterone axis of tetrapods. This would account for some of the similarities between ablation of the STANNIUS corpuscles and interrenalectomy in eels,
though the effects of the two operations are not completely identical; both procedures result in a decreased plasma sodium level, but only ablation of the corpuscles
produces the elevated potassium and calcium concentrations (CHAN et al., 1967a).
Endocrine tissues usually have been found to have several roles and secretions; this
could also apply to the corpuscles of STANNIUS.
b) The Caudal Neurosecretory System and the Urophysis
Neurosecretory nerve fibres have been histologically identified in the caudal
regions of the spinal cord in a number of fishes . The literature has been reviewed
by FRIDBERG and BERN (1968). These neurons (DAHLGREN cells) were described
by SPEIDEL (1919) in chondrichthyeans. ENAMI(1955) described a discrete bundle
of such cells in the japanese eel, Anguilla japonica, where they form a distinct lobe
of neurosecretory cells abutting onto a bed of capillaries to form a neurohaemal
junction. The degree of aggregation of such cells to form a lobate-structure, the
urophysis, differs in various species, and achieves its most distinct form in certain
teleosts. In the Chondrichthyes the cells are situated in a diffuse area, which in
Raja batis, may extend over the area of the last 55 vertebrae. These caudal neurosecretory fibres have only been identified in the Chondrichthyes, releostean and
chondrostean bon y fishes.
The neurosecretory cells in the caudal regions of fish, and those of the hypothalame-neurohypophysial region of the vertebrate brain, are analogous in their general histological properties. However, the caudal cells, in contrast to the cephalic
ones, do not produce secretions that can be stained with iron-alum haematoxylin.
Both groups of neurosecretory material are thought to be protein-like. The caudal
neurosecretory neurons, like typical neurosecretory cells, can transmit nerve impulses (MORITA, ISHIBASHI, and YAMASHITA, 1961).
An endocrine role for the caudal neurosecretory cells remains to be established.
Their possible role in osmoregulation has been explored, probably partly as a result
of their morphological analogies with the neurohypophysis. Extirpation of the
urophysis in some teleosts has failed to reveal evidence for such a function, but
the potential regeneration of such tissues makes such available evidence inconclusive (FRIDBERG and BERN, 1968). MAETZ, BOURGUET, and LAHLOUH (1963)
found that when extracts of the urophysis were reinjected into the goldfish, Carassiusauratus, there was an increased branchial uptake of sodium and an increased
urine flow, with a reduced renal loss of sodium. These experiments need extending
to other species of fish before any general conclusions can be drawn, but at the
79