8o iii. 8 — ill. 9. 



as the covering which invests them is dense and shell-Hke, 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- 

 tortoises a large one, the land-tortoises an extremely small onc.^ 



(Ch. g.) 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 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 distributed over several regions.^ 



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. 



In the centre of the kidney is a cavity of variable size. This is 

 the case in all animals, excepting the seal.^ The kidneys of this 

 animal are more solid than those of any other, and in form 

 resemble the kidneys of the ox. The human kidneys are of 

 similar shape ; being as it were made up of numerous small 

 kidneys,^ and not presenting one unbroken surface like the 

 kidneys of sheep and other quadrupeds.''' For this reason, 

 should the kidneys of a man be once attacked by disease, the 

 malady is not easily expelled. For it is as though many kidneys 

 were diseased and not merely one ; which naturally enhances the 

 difficulties of a cure. 



The duct which runs to the kidney from the great vessel does 

 not terminate in the central cavity, but is expended in the 

 substance of the organ, so that there is no blood in the cavity, 

 nor is any coagulum found there after death. A pair of stout ducts, 

 void of blood, run, one from the cavity of each kidney, to the 

 bladder; and other ducts, strong and continuous, lead into the 

 kidneys from the aorta.^ The purpose of this arrangement is to 

 671b. 



