PARTS OF ANIMALS, III. viii.-ix. 



cannot do so, because the integument which surrounds 

 them is dense, hke a shell ; and so the excretion is 

 produced in such quantities that the Tortoises need 

 some part which shall act as a vessel to receive it. 

 That, then, is why they are the only animals of the 

 kind which have a bladder. In the sea-tortoise it is 

 large, in the land-tortoise quite small. 



IX. Much the same may be said of the kidneys as Kidneyts. 

 of the bladder. Kidneys are not present in any of 

 the animals that have feathers or scales or scaly plates, 

 except the two sorts of tortoises just mentioned. In 

 some birds, how^ever, there are flat Iddney-shaped 

 objects, as if the flesh that was allotted to form the 

 kidneys had found no room for its proper function 

 and had been scattered to form several organs. The 

 Emys ^ has neither bladder nor kidneys : this is be- 

 cause it has a soft shell which allows the moisture to 

 transpire freely through it. But, as I said before, all 

 the other animals whose lung contains blood have 

 kidneys, since Nature makes use of them for two pur- 

 poses : (1) to subserve the blood-vessels ; and (2) to 

 excrete the fluid residue. (A channel leads into them 

 from the Great Blood-vessel.) 



There is always a hollow (lumen), varying in size, 

 in the kidneys, except in the seal, whose kidneys are 

 more solid than any others and in shape resemble 

 those of the ox. Human kidneys too resemble those 

 of the ox : they are, as it were, made up out of a 

 number of small kidneys,^ and have not an even 

 surface like those of the sheep and other quadrupeds. 

 Thus, when once an ailment attacks the human 



any animal now known as Emys, seems to be that of some 

 freshwater tortoise. 



'' This is not true of the normal adult, but it is true of 

 the foetus. 



274 



