olis carolinensis, and with more fruitful results than have been achieved in vitro.
Removal of segments of the adenohypophysis resulted in the disappearance of corticosterone from the circulation. The administration of dexamethasone also had
this effect, suggesting the presence of a negative feed -back system controlling the
release of corticotrophin. When mammalian corticotrophin was injected into lizards so treated with dexamethasone, corticosterone reappeared in the plasma. Extracts from the adenohypophyses of Anolis as well as the desert lizard, Dipsosaurus
dorsalis, the slider turtle, Pseudemys scripta, and the caiman have a similar action,
indicating the p resence of a corticotrophic principle in their pituitaries.
The possibility of the presence of an additional control mechanism involving
renin and angiotensin does not yet appear to have been investigated in the reptiles.
However, renin-like activity has been identified in the kidneys of the freshwater
turtle, Chrysemys picta, and the desert tortoise, Gopherus agassizii, (CAPELLI et al.,
1970). Such a system could have an Important role , for in other vertebrates angiotensin has a potent stimulating action on the production of corticosterone as well
as aldosterone. As in the instance of the neurohypophysis, knowledge of the physiology of the hormones from the adrenocortical tissue of reptiles is less complete
than in any other tetrapod group.
3. The Accumulation of Water and Salts
Water and salts are acquired by reptiles in the usual manner, from their food and
drink.
Since amphibians do not drink, the reptiles represent phyletically the first tetrapods to utilize this osmotically useful habit. Certain aquatic reptiles, such as the
caiman and softshell turtle, also acquire substantial amounts of water by osmosis
through their skin, but the skin of most reptiles seems to be relatively impermeable, so that water uptake in this way is not usually important. The possibility
that some terrestrial reptiles may accumulate water through their skin has been
the subject of speculation which has not been confirmed in v iv o. The mountain
devil, Moloch borridus, an agamid lizard thatlives in the desert regions of Australia,
was once popularly thought to absorb water through its skin. When these lizards
are placed in water it flows onto the integument, giving it the appearance of damp
blotting paper, but absorption through the skin does not take place. Instead, water
can be taken from the skin into the mouth, a process accompanied by 'chewing'
movements of the jaws (BENTLEY and BLUMER, 1962). These lizards can accumulate
water in this way but are never seen to drink in the more conventional manner.
Such a procedure may be useful in desert reptiles, as it would allow them to gather
water from sources too sparse to collect from otherwise. Drinking may occur only
sporadically in desert reptiles ; as described earlier the Australian lizards, Amphibolurus ornatus, have been observed to rush about drinking avidly when an infrequent
shower of rain falls. Such rapid sporadic drinking probably allows many reptiles
to make periodic osmotic adjustments. SCHMIDT-NIELSEN (1964 a) has described
the beha viour of a desert tortoise which, in a single session, drank water equivalent
to 40% of its bod y weight and DARWIN (1839) has commented on the prominent
drinking habits of the tortoises of th e Galapagos Islands. It is possible that certain
157
Removal of segments of the adenohypophysis resulted in the disappearance of corticosterone from the circulation. The administration of dexamethasone also had
this effect, suggesting the presence of a negative feed -back system controlling the
release of corticotrophin. When mammalian corticotrophin was injected into lizards so treated with dexamethasone, corticosterone reappeared in the plasma. Extracts from the adenohypophyses of Anolis as well as the desert lizard, Dipsosaurus
dorsalis, the slider turtle, Pseudemys scripta, and the caiman have a similar action,
indicating the p resence of a corticotrophic principle in their pituitaries.
The possibility of the presence of an additional control mechanism involving
renin and angiotensin does not yet appear to have been investigated in the reptiles.
However, renin-like activity has been identified in the kidneys of the freshwater
turtle, Chrysemys picta, and the desert tortoise, Gopherus agassizii, (CAPELLI et al.,
1970). Such a system could have an Important role , for in other vertebrates angiotensin has a potent stimulating action on the production of corticosterone as well
as aldosterone. As in the instance of the neurohypophysis, knowledge of the physiology of the hormones from the adrenocortical tissue of reptiles is less complete
than in any other tetrapod group.
3. The Accumulation of Water and Salts
Water and salts are acquired by reptiles in the usual manner, from their food and
drink.
Since amphibians do not drink, the reptiles represent phyletically the first tetrapods to utilize this osmotically useful habit. Certain aquatic reptiles, such as the
caiman and softshell turtle, also acquire substantial amounts of water by osmosis
through their skin, but the skin of most reptiles seems to be relatively impermeable, so that water uptake in this way is not usually important. The possibility
that some terrestrial reptiles may accumulate water through their skin has been
the subject of speculation which has not been confirmed in v iv o. The mountain
devil, Moloch borridus, an agamid lizard thatlives in the desert regions of Australia,
was once popularly thought to absorb water through its skin. When these lizards
are placed in water it flows onto the integument, giving it the appearance of damp
blotting paper, but absorption through the skin does not take place. Instead, water
can be taken from the skin into the mouth, a process accompanied by 'chewing'
movements of the jaws (BENTLEY and BLUMER, 1962). These lizards can accumulate
water in this way but are never seen to drink in the more conventional manner.
Such a procedure may be useful in desert reptiles, as it would allow them to gather
water from sources too sparse to collect from otherwise. Drinking may occur only
sporadically in desert reptiles ; as described earlier the Australian lizards, Amphibolurus ornatus, have been observed to rush about drinking avidly when an infrequent
shower of rain falls. Such rapid sporadic drinking probably allows many reptiles
to make periodic osmotic adjustments. SCHMIDT-NIELSEN (1964 a) has described
the beha viour of a desert tortoise which, in a single session, drank water equivalent
to 40% of its bod y weight and DARWIN (1839) has commented on the prominent
drinking habits of the tortoises of th e Galapagos Islands. It is possible that certain
157