166 ARISTOTLE S ANHOMCEOMERIA 



ones. In some land tortoises the bladder is a large reservoir 

 furnishing them with moisture when at a distance from 

 their usual drinking places ; this is well exemplified by 

 Darwin in his Naturalist s Voyage round the World (2nd 

 edition, London, 1890, p. 409). With respect to Aristotle s 

 statement about the form of the kidneys of tortoises, it may 

 be said that these kidneys are compact but present a series 

 of convolutions, e.g., the surface of each kidney of a small 

 specimen of the Grecian tortoise showed a series of ridges and 

 furrows, and, when the capsule was removed, the substance 

 of the kidney showed the ridges and furrows very clearly 

 indeed, the whole forming a pattern scarcely less complicated 

 than that seen on the surface of the human brain. 



Aristotle says that, in all animals, the right kidney is 

 higher or more forward than the left, and is drier and less 

 fatty.* The right kidney is generally nearer the head than 

 the left in mammals and in the grass-snake and some other 

 snakes. In Man and the pig the left kidney is often a little 

 nearer the head than the right, while the kidneys of most 

 birds, of some pigs and sheep, and of the frog and some 

 other animals, are as nearly as possible symmetrical in 

 position. The amount of fat about the kidneys varies much, 

 even in individuals of the same species. In sheep, pigs, and 

 some other animals, it may be said that, when the kidneys 

 are unsymmetrical in position, the amount of fat about the 

 one which is nearer the head is greater than that about the 

 other. 



It has been shown how, contrary to the modern opinion, 

 Aristotle subordinated the kidneys to the bladder ; in a 

 somewhat similar way he subordinated the testes to the 

 seminal ducts. This w T ill be clear from the following 

 epitome of G. A. i. c. 4: The testes are not necessary for 

 reproductive purposes, for, if they were, they would be found 

 in all animals which reproduce. Now, neither snakes nor 

 fishes have testes, yet their poroi (ducts) are full of semen. 

 The testes, in fact, serve a kind of regulating purpose only, 

 and are not parts of the poroi, but attachments, just like the 

 stones which weavers attach to the warp, and, when the 

 testes are removed, the poroi are withdrawn backwards. 

 Hence, in such a case, the poroi are withdrawn and the 

 animal becomes impotent, but, in one instance, a bull was 

 temporarily potent because the poroi were not withdrawn. 



* H. A. i.e. 14,3,7. 



