Again,

all viviparous quadrupeds are furnished with kidneys and
a bladder. Of the ovipara that are not quadrupedal there is no
instance known of an animal, whether fish or bird, provided with these
organs. Of the ovipara that are quadrupedal, the turtle alone is
provided with these organs of a magnitude to correspond with the other
organs of the animal. In the turtle the kidney resembles the same
organ in the ox; that is to say, it looks one single organ composed of
a number of small ones. (The bison also resembles the ox in all its
internal parts).