PARTS OF ANIMALS, I. v. 



First of all, our business must be to describe the Final 

 attributes found in each group ; I mean those of the 

 " essential " attributes which belong to all the -^i^^thod. 

 animals, and after that to endeavour to describe the 

 causes of them. It will be remembered that I have 

 said already that there are many attributes which 

 are common to many animals, either identically the 

 same {e.g. organs like feet, feathers, and scales, and 

 affections similarly), or else common by analogy 

 only {i.e. some animals have a lung," others have no 

 lung but something else to correspond instead of 

 it ; again, some animals have blood, while others have 

 its counterpart,^ which in them has the same value 

 as blood in the former). And I have pointed out 

 above that to treat separately of all the particular 

 species would mean continual repetition of the 

 same things, if we are going to deal with all their 

 attributes, as the same attributes are common to 

 many animals. Such, then, are my views on this 

 matter. 



Now, as each of the parts of the body, like every 

 other instrument, is for the sake of some purpose, 

 viz. some action, it is evident that the body as a 

 whole must exist for the sake of some complex 

 action. Just as the saw is there for the sake of 

 sawing and not sawing for the sake of the saw, 

 because sawing is the using of the instrument, so in 

 some way the body exists for the sake of the soul, 

 and the parts of the body for the sake of those 

 functions to which they are naturally adapted. 



So first of all we must describe the actions (a) 



larvae (Chironomiis), worms (Arenicola). In other in- 

 vertebrates the blood may be bhie (Crustacea) or green 

 (Sabellid worms), or there may be no respiratory pigment 

 at all (most insects). 



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