that bathes them, so that an active transport of sodium in such regions could mediate a net accumulation of this ion by turtles. In the softshell turtle DUNSON considers that active sodium transport across the pharynx may be responsible for such
solute collection.
d) 'Salt' Glands
"'So they went up to the Mock turtle who looked at them with large eyes full of
tears'; 'for I am the crocodile' and he wept crocodile-tears to show it was quite
true'''. These two quotations from LEWIS CARROLL and RUDYARD KIPLING introduce a delightful account by SCHMIDT-NIELSEN and FANGE (1958) of their discovery of the salt secreting supraorbital ('tear') glands in reptiles. The diamondback
terrapin, Malaclemys centrata, and the loggerhead turtle, Caretta caretta , secretehighly concentrated salt solutions from such tear (Harderian) glands, situated in
the orbit. The marine iguana, Amblyrhynchus cristatus, of the Galapagos islands
utilizes a nasal gland for this purpose, just as in the birds. Crocodiles, however,
have not been shown to secrete such salty 'tears'. Other marine reptiles that utilize
'salt' glands for electrolyte excretion are: the yellow-banded sea snake, Laticauda
semzfasciata, and the yellow-bellied sea snake, Pelamis platurus, in which the particular tissue concerned appears to be an Harderian gland (DUNSON and T AUB, 1967;
DUNSON, 1968).
SCHMIDT-NIELSEN and his collaborators (1963) also found functioning nasal
salt glands in a number of terrestrial lizards; the tropical iguana, Iguana iguana,
the desert iguana, Dipsosauras dorsalis, and the North African desert lizard
Uromastyx aegyptus. Such secretory glands have also been demonstrated in the
North American lizards : the chuckawalla, Sauromalus obesus, the false iguana,
Ctenosaura pectinata, and the blue spmy lizard, Sceloporus dorsalis, (TEMPLETON,
1964 and 1966), as well as a lizard, Uromastyx acanthinurus, that lives in the Sahara
(GRENOT, 1967). Such functioning secretory glands are not, however, present in
all terrestrial reptiles, nor when present, do they all function with similar efficiency'.
The fluid produced by such salt glands in reptiles is many times more concentrated than the blood plasma while the electrolyte levels in the secretions from
marine species are even higher than those in sea-water (Table 5.8). Reptiles with
such accessory salt secreting organs can thus excrete the salts from a varied marine
diet, and probably even drink some sea-water without incurring a deficit in their
body water. While in marine reptiles the sodium concentrations present in the salt
gland secretions are much higher than those of potassium (Na/K as much as 20/1),
the terrestriallacertilians usually secrete a relatively potassium-rich fluid, Na/K<
0.1 . Such an arrangement is consistent with the relative abundance of these ions
in the diets of marine and terrestrial species.
The stimuli that inititiate secretion by the salt glands of reptiles appear to be
similar to those seen in birds. Injections of hyperosmotic solutions of sodium chloride, potassium chloride or sucrose and the cholinergic drug methacholine can
all bring about secretion. It is interesting that even in terrestrial lizards, in which
potassium is the predominant ion present, injections of sodium chloride still have
a kalitropic action (TEMPLETON, 1964 and 1966). However, after such administra152
solute collection.
d) 'Salt' Glands
"'So they went up to the Mock turtle who looked at them with large eyes full of
tears'; 'for I am the crocodile' and he wept crocodile-tears to show it was quite
true'''. These two quotations from LEWIS CARROLL and RUDYARD KIPLING introduce a delightful account by SCHMIDT-NIELSEN and FANGE (1958) of their discovery of the salt secreting supraorbital ('tear') glands in reptiles. The diamondback
terrapin, Malaclemys centrata, and the loggerhead turtle, Caretta caretta , secretehighly concentrated salt solutions from such tear (Harderian) glands, situated in
the orbit. The marine iguana, Amblyrhynchus cristatus, of the Galapagos islands
utilizes a nasal gland for this purpose, just as in the birds. Crocodiles, however,
have not been shown to secrete such salty 'tears'. Other marine reptiles that utilize
'salt' glands for electrolyte excretion are: the yellow-banded sea snake, Laticauda
semzfasciata, and the yellow-bellied sea snake, Pelamis platurus, in which the particular tissue concerned appears to be an Harderian gland (DUNSON and T AUB, 1967;
DUNSON, 1968).
SCHMIDT-NIELSEN and his collaborators (1963) also found functioning nasal
salt glands in a number of terrestrial lizards; the tropical iguana, Iguana iguana,
the desert iguana, Dipsosauras dorsalis, and the North African desert lizard
Uromastyx aegyptus. Such secretory glands have also been demonstrated in the
North American lizards : the chuckawalla, Sauromalus obesus, the false iguana,
Ctenosaura pectinata, and the blue spmy lizard, Sceloporus dorsalis, (TEMPLETON,
1964 and 1966), as well as a lizard, Uromastyx acanthinurus, that lives in the Sahara
(GRENOT, 1967). Such functioning secretory glands are not, however, present in
all terrestrial reptiles, nor when present, do they all function with similar efficiency'.
The fluid produced by such salt glands in reptiles is many times more concentrated than the blood plasma while the electrolyte levels in the secretions from
marine species are even higher than those in sea-water (Table 5.8). Reptiles with
such accessory salt secreting organs can thus excrete the salts from a varied marine
diet, and probably even drink some sea-water without incurring a deficit in their
body water. While in marine reptiles the sodium concentrations present in the salt
gland secretions are much higher than those of potassium (Na/K as much as 20/1),
the terrestriallacertilians usually secrete a relatively potassium-rich fluid, Na/K<
0.1 . Such an arrangement is consistent with the relative abundance of these ions
in the diets of marine and terrestrial species.
The stimuli that inititiate secretion by the salt glands of reptiles appear to be
similar to those seen in birds. Injections of hyperosmotic solutions of sodium chloride, potassium chloride or sucrose and the cholinergic drug methacholine can
all bring about secretion. It is interesting that even in terrestrial lizards, in which
potassium is the predominant ion present, injections of sodium chloride still have
a kalitropic action (TEMPLETON, 1964 and 1966). However, after such administra152