Moreover,
inasmuch as the covering which invests them is dense and shell-like,
so that the moisture cannot exhale through the porous flesh, as it
does in birds and in snakes and other animals with scaly plates,
such an amount of secretion is formed that some special part is
required to receive and hold it. This then is the reason why these
animals, alone of their kind, have a bladder, the sea-tortoise a large
one, the land-tortoises an extremely small one.
9
What has been said of the bladder is equally true of the kidneys.
For these also are wanting in all animals that are clad with
feathers or with scales or with scale-like plates; the sea and land
tortoises forming the only exception. In some of the birds, however,
there are flattened kidney like bodies, as though the flesh allotted
to the formation of the kidneys, unable to find one single place of
sufficient size, had been scattered over several.
The Emys has neither bladder nor kidneys. For the softness of its
shell allows of the ready transpiration of fluid; and for this
reason neither of the organs mentioned exists in this animal. All
other animals, however, whose lung contains blood are, as before said,
provided with kidneys. For nature uses these organs for two separate
purposes, namely for the excretion of the residual fluid, and to
subserve the blood-vessels, a channel leading to them from the great
vessel.
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