PARTS OF ANIiMALS 



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 

 two stages of difference : 



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

 defect " — as in different species of the same 

 genus or group. 

 (6) 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 11-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 what (again in the Aristotehan 

 sense) we term ' specific ' differences " {Growth and 



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

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

 groups. 



15 



