at least some steroid hormones'. She also considers it possible that they could 'convert plasma steroids, synthesized elsewhere, into other active hormones a process
which might be called "cooperative steroidogenesis". CHESTER JONES et al. (1966;
1969 b) have found that corpuscular extracts from eels, when injected, raise the
blood pressure of rats or eels. The extracts contain material that behaves in many
respects like mammalian renin and they have suggested that it may function like
the tetrapod renin-angiotensin system does in controlling the secretion of aldosterone. The effects of ablation of the corpuscles of STANNIUS on plasma sodium levels
and their partial correction with aldosterone would also be consistent with this
suggestion. Eels do not produce aldosterone but another steroid could be involved.
The corpuscular material that influences calcium metabolism in eels is presumably
a separate principle.
6. Osmoregulation and the Endocrines in Some Relict Fishes
a) The Lungfishes (Dipnoi)
These bony fishes originated in fresh water during Devonian times, about 320 million years ago. Although in the past a few species have lived in the sea, they have
remained an essentiall y freshwater group. Their ability to withstand transfer to seawater does not, however, appear to have been reported. Today they are represented
by two phyletic groups : the Ceratodontidae and the Lepidosirenidae. The former
contains one species, Neoceratodus [orsteri, which is confined to rivers in a small
area of Queensland in Australia. The Lepidosirenidae contain two genera; Protopterus which lives in Africa and Lepidosiren in South America. Information about
the water and salt metabolism of this group is, as far as I can ascertain, entirely
confined to Protopterus. HOMER SMITH made some fascinating observations on
the osmoregulation of these fish and an enjoyable account of his travels in search
of them are described in 'Kamongo or the Lungfish and the Padre' (H. SMITH,
1956).
The lungfishes appear to have a normal complement of endocrine glands,
though these have not been exhaustively examined. The neurohypophyses of all
three genera contain vasotocin, but, in contrast to other bony fishes, mesotocin
and sometimes oxytocin, instead of isotocin. These peptides also occur in the Amphibia and the neurohypophysis of lungfish bears some morphological similarity
to the amphibian gland (WINGSTRAND, 1966). Cortisol has been identified in the
circulation of Protopterus (PHILLIPS and CHESTER JONES, 1957), while corticosterone can be formed by incubates of its adrenocortical tissues in vitro (JANSSENS
et al., 1965). As aldosterone has not been found, this arrangement is more fishlike,
though the tissues that form these steroids are morphologically like those 'of a
primitive amphibian ' (JANSSENS et al., 1965). MOORHOUSE (1956) found that the
'adrenocortical' tissues of Protopterus regress following hypophysectom y while
the injection of mammalian corticotrophin stimulated them. JANSSENS et al. also
found that these tissues hypertrophied in response to injections of corticotrophin
and regressed following administration of cortisol. They thus appear to behave like
the adrenocortical tissues of other vertebrates and, at least partly, are under the
control of the adenohypophysis. The pituitary also contains a prolactin-like hor246
which might be called "cooperative steroidogenesis". CHESTER JONES et al. (1966;
1969 b) have found that corpuscular extracts from eels, when injected, raise the
blood pressure of rats or eels. The extracts contain material that behaves in many
respects like mammalian renin and they have suggested that it may function like
the tetrapod renin-angiotensin system does in controlling the secretion of aldosterone. The effects of ablation of the corpuscles of STANNIUS on plasma sodium levels
and their partial correction with aldosterone would also be consistent with this
suggestion. Eels do not produce aldosterone but another steroid could be involved.
The corpuscular material that influences calcium metabolism in eels is presumably
a separate principle.
6. Osmoregulation and the Endocrines in Some Relict Fishes
a) The Lungfishes (Dipnoi)
These bony fishes originated in fresh water during Devonian times, about 320 million years ago. Although in the past a few species have lived in the sea, they have
remained an essentiall y freshwater group. Their ability to withstand transfer to seawater does not, however, appear to have been reported. Today they are represented
by two phyletic groups : the Ceratodontidae and the Lepidosirenidae. The former
contains one species, Neoceratodus [orsteri, which is confined to rivers in a small
area of Queensland in Australia. The Lepidosirenidae contain two genera; Protopterus which lives in Africa and Lepidosiren in South America. Information about
the water and salt metabolism of this group is, as far as I can ascertain, entirely
confined to Protopterus. HOMER SMITH made some fascinating observations on
the osmoregulation of these fish and an enjoyable account of his travels in search
of them are described in 'Kamongo or the Lungfish and the Padre' (H. SMITH,
1956).
The lungfishes appear to have a normal complement of endocrine glands,
though these have not been exhaustively examined. The neurohypophyses of all
three genera contain vasotocin, but, in contrast to other bony fishes, mesotocin
and sometimes oxytocin, instead of isotocin. These peptides also occur in the Amphibia and the neurohypophysis of lungfish bears some morphological similarity
to the amphibian gland (WINGSTRAND, 1966). Cortisol has been identified in the
circulation of Protopterus (PHILLIPS and CHESTER JONES, 1957), while corticosterone can be formed by incubates of its adrenocortical tissues in vitro (JANSSENS
et al., 1965). As aldosterone has not been found, this arrangement is more fishlike,
though the tissues that form these steroids are morphologically like those 'of a
primitive amphibian ' (JANSSENS et al., 1965). MOORHOUSE (1956) found that the
'adrenocortical' tissues of Protopterus regress following hypophysectom y while
the injection of mammalian corticotrophin stimulated them. JANSSENS et al. also
found that these tissues hypertrophied in response to injections of corticotrophin
and regressed following administration of cortisol. They thus appear to behave like
the adrenocortical tissues of other vertebrates and, at least partly, are under the
control of the adenohypophysis. The pituitary also contains a prolactin-like hor246