GENT:RATI0N of animals, v. vm. 



bone, those of the front teeth are in a thin part, and 

 in consequence the teeth are weak and can easily be 

 removed. They grow a second time, because thev 

 are shed while the bone is still growing and while 

 the age for growing teeth is still going on. A proof 

 of this is that even the flat teeth take a long time 

 growing : the last of them are cut at about twenty 

 years of age ; in fact, some people have been quite 

 aged before their last teeth finished growing. The 

 reason for this is that there is a great deal of nourish- 

 ment in the wide part of the bones. The front part, 

 however, quickly reaches its completion owing to its 

 thinness, and no residue finds a place in it ; instead 

 of that, the nourishment is consumed to supply that 

 part's own growth. 



Democritus, however, omitted to mention the Necessity 

 Final Cause," and so all the things which Nature p^naic^aus 

 employs he refers to necessity. It is of course true 

 that they are determined by necessity, but at the 

 same time they are for the sake of some purpose, 

 some Final Cause, and for the sake of that which is 

 better in each case.* And so there is nothing to 

 prevent the teeth being formed and being shed in 

 the way he says "^ ; but it is not on that account that 

 it happens, but on account of the Final Cause, the 

 End ; those other factors are causes' qua causing 

 movement, qua instruments, and qua material, 

 since in fact it is probable that Nature makes the 

 majority of her productions by means of pneuma ^ 

 used as an instrument. Pneuma serves many uses 

 in the things constructed by Nature, just as certain 

 objects do in the arts and crafts, e.g., the hammer 

 and an\-il of the smith. But to allege that the 

 causes are of the necessary type is on a par with 



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