PARTS OF ANIMALS 



characteristic (642 b 10 foil.). The right method, 

 says Aristotle, is to follow popular usage and divide 

 the animals up into well-defined groups such as 

 Birds and Fishes." And this leads him to distinguish 

 tΛvo stages of difference : 



(a) Cases in Λvhich the parts differ " by excess or 

 defect " — as in different species of the same 

 genus or group. 



(b) Cases in which the resemblance is merely one 

 of analogy — as in different genera. 



Examples of (a) : differences of colour and shape ; 



many or few ; large or small ; 



smooth or rough ; e.g. soft and 



firm flesh, long and short bill, 



many or few feathers. 

 (b) bone and fish-spine ; nail and 



hoof ; hand and claw ; scale and 



feather. 

 (Reff. for the above, De part. an. 644. a 1 1-b 15 ; Hist, 

 an. 486 a 15-b 21. See also Gen. An. (Loeb), Introd.) 



The doctrine of differences of" excess and defect," "The more 

 or, as Aristotle also calls them, of " the more and ^° '®^^• 

 less," may usefully be compared with that which 

 underlies the modern theory of Transformations, and 

 the comparison of related forms. Indeed, Professor 

 D'Arcy Thompson asserts that " it is precisely . . . 

 this Aristotelian ' excess and defect ' in the case 

 of form which our co-ordinate method is especially 

 adapted to analyse, and to reveal and demonstrate 

 as the main cause of Λvhat (again in the AristoteUan 

 sense) Λve term * specific ' differences " (Gronih and 



" And of course, into Blooded and Bloodless, though there 

 are, as Aristotle points out, no popular names for these 

 groups. 



19 



