(McFARLAND and MUNZ, 1965) consider the Pacific hagfish to be isoosmotic to
sea-water. Whatever the source, water is secreted in the urine of both species and
this is isoosmotic (or very nearly so) with the plasma, and contains slightly lower
levels of sodium but higher concentrations of divalent ions . Sodium and water
reabsorption do not appear to take place from the renal tubule, but glucose is conserved and potassium and divalent ions may be secreted by the tubules (MUNZ and
McFARLAND, 1964). The latter workers have also pointed out the considerable differences that exist between the ionic composition of the plasma and the secretions
of the integumental mucous glands in hagfish (see Table 7.13). They have suggested
that these ma y afford an additional avenue for ionic excretion. Thus the kidneys,
and possibly the mucous glands, contribute to the maintenance of the composition
of the extracellular fluids, slight though the differences from sea-water may seem.
Despite their low position on the phyletic scale the hagfishes possess endocrine
tissues and 'hormones' similar to those present in other vertebrates. Cortisol and
corticosterone, but not aldosterone, have been found in the blood of both the Atlantic and Pacific hagfishes and in concentrations similar to those which occur in
mammals (CHESTER JONES and PHILLIPS, 1960; PHILLIPS et al., 1962 b). However,
using more recently developed techniques WEISBART and IDLER (1970) have been
unable to detect these steroids in Atlantic hagfishes or sea lampreys so that a reevaluation of the potential role of corticosteroids in cyclostomes may be necessary.
The pituitary gland of Myxine glutinosa contains an activity that, like corticotrophin, stimulates the growth of adrenocortical tissues in immature mice (STRAHAN, 1959). In addition, this gland contains a peptide that behaves in many ways
like vasotocin (FOLLETT and HELLER, 1964 b). The endocrine products present in
the Myxinoidea are thus distinctly similar to those in higher vertebrates, but this
appears to be the end of their phyletic existence; thus corticosteroids have not been
found in th e protochordate Amphioxus (CHESTER JONES and PHILLIPS, 1960), while
despite earlier reports, neurohypophysial pep tides are not present in ascidians
(SAWYER, 1959).
The hagfishes show evidence of osmoregulatory activity, but this seems to exist
principally at the barrier between the cell and the extracellular fluid. The integument is relatively impermeable to sodium and there is no evidence to suggest
that active uptake or extrusion of ions can occur across the skin or gills of hagfishes .
Some osmoregulation occurs as a result of the activities of the kidneys and mucous
glands but there is no information about the action of hormones on their secretions.
When hagfishes are placed in dilute sea-water sodium loss is restricted but the y
accumulate large amounts of water. This is subsequently excreted indicating that
'volume regulation' is occurring. As M cFARLAND and MUNZ (1965) indicate, this
may be an ' aut omatic' process due to an increased GFR resulting from the dilution
of plasma proteins.
CHESTER JONES, PHILLIPS, and BELLAMY (1962) measured the effects of various
hormone preparations on the water and electrolyte composition of Myxine glutinosa. In order to promote the need for regulatory action the y placed the fish in dilute (60%) sea-water and then injected them, over a period of several days, with
the hormones. Aldosterone, deoxycorticosterone and corticotrophin decreased the
levels of sodium in the muscle, though the plasma concentrations were unchanged.
Mammalian prolactin (a 'prolactin' has not been found in the Agnatha!) had a simi253
sea-water. Whatever the source, water is secreted in the urine of both species and
this is isoosmotic (or very nearly so) with the plasma, and contains slightly lower
levels of sodium but higher concentrations of divalent ions . Sodium and water
reabsorption do not appear to take place from the renal tubule, but glucose is conserved and potassium and divalent ions may be secreted by the tubules (MUNZ and
McFARLAND, 1964). The latter workers have also pointed out the considerable differences that exist between the ionic composition of the plasma and the secretions
of the integumental mucous glands in hagfish (see Table 7.13). They have suggested
that these ma y afford an additional avenue for ionic excretion. Thus the kidneys,
and possibly the mucous glands, contribute to the maintenance of the composition
of the extracellular fluids, slight though the differences from sea-water may seem.
Despite their low position on the phyletic scale the hagfishes possess endocrine
tissues and 'hormones' similar to those present in other vertebrates. Cortisol and
corticosterone, but not aldosterone, have been found in the blood of both the Atlantic and Pacific hagfishes and in concentrations similar to those which occur in
mammals (CHESTER JONES and PHILLIPS, 1960; PHILLIPS et al., 1962 b). However,
using more recently developed techniques WEISBART and IDLER (1970) have been
unable to detect these steroids in Atlantic hagfishes or sea lampreys so that a reevaluation of the potential role of corticosteroids in cyclostomes may be necessary.
The pituitary gland of Myxine glutinosa contains an activity that, like corticotrophin, stimulates the growth of adrenocortical tissues in immature mice (STRAHAN, 1959). In addition, this gland contains a peptide that behaves in many ways
like vasotocin (FOLLETT and HELLER, 1964 b). The endocrine products present in
the Myxinoidea are thus distinctly similar to those in higher vertebrates, but this
appears to be the end of their phyletic existence; thus corticosteroids have not been
found in th e protochordate Amphioxus (CHESTER JONES and PHILLIPS, 1960), while
despite earlier reports, neurohypophysial pep tides are not present in ascidians
(SAWYER, 1959).
The hagfishes show evidence of osmoregulatory activity, but this seems to exist
principally at the barrier between the cell and the extracellular fluid. The integument is relatively impermeable to sodium and there is no evidence to suggest
that active uptake or extrusion of ions can occur across the skin or gills of hagfishes .
Some osmoregulation occurs as a result of the activities of the kidneys and mucous
glands but there is no information about the action of hormones on their secretions.
When hagfishes are placed in dilute sea-water sodium loss is restricted but the y
accumulate large amounts of water. This is subsequently excreted indicating that
'volume regulation' is occurring. As M cFARLAND and MUNZ (1965) indicate, this
may be an ' aut omatic' process due to an increased GFR resulting from the dilution
of plasma proteins.
CHESTER JONES, PHILLIPS, and BELLAMY (1962) measured the effects of various
hormone preparations on the water and electrolyte composition of Myxine glutinosa. In order to promote the need for regulatory action the y placed the fish in dilute (60%) sea-water and then injected them, over a period of several days, with
the hormones. Aldosterone, deoxycorticosterone and corticotrophin decreased the
levels of sodium in the muscle, though the plasma concentrations were unchanged.
Mammalian prolactin (a 'prolactin' has not been found in the Agnatha!) had a simi253