PARTS OF ANIMALS 



to A (2) above — the parts common to a group 



of animals, and we have first : 



The Internal Parts of Blooded Animals. 



III. This is folloAved by — 



The Internal Parts of Bloodless Animals. Then, 



IV. The External Parts of Bloodless Animals. Then, 

 V. The External Parts of Blooded Animals, 



which includes — 



(a) Vivipara. 

 (6) Ovipara. 



(i) Serpents and Quadrupeds. 

 (ii) Birds. 

 (iii) Fishes, 

 (c) Intermediate Creatures. 



References to exceptional instances, as to Man, 

 corresponding to the division A (3) above, are of 

 course to be found throughout the Avork, 



Aristotle thus works out the main lines of his 

 classification. And in each instance, where possible, 

 he endeavours to assign the Cause, to name the 

 purpose, which is responsible for the parts as he 

 describes them. This corresponds to (B) above. 



And here Aristotle is forced to admit an apparent Necessity. 

 addition to his scheme of Causes. The purpose, the 

 good End, the final Cause, cannot always get a free 

 hand. There is another Cause, Necessity. Aristotle 

 takes great care to explain what is the nature of this 

 Necessity (642 a 2 foil.). It is what he calls Necessity 

 " ex hypothesi," or " conditional " Necessity, the sort 

 of Necessity which is implied by any final Cause 

 being what it is. If a piece of wood is to be spUt 

 by an axe, the axe must ex hypothesi be hard and 

 sharp, and that necessitates the use of bronze or 



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