ARISTOTLE. 45 



of the Universe. His ' perfecting principle ' in 

 Nature is only one of a score of his legacies to 

 later speculation upon Evolution causation. Many 

 of our later writers are Aristotelians without appar- 

 ently being conscious of it. 



Let us first look at Aristotle's equipment as a 

 naturalist. He enters a plea for the study and dis- 

 section of lower types : " Hence we ought not with 

 puerile fastidiousness to neglect the contemplation 

 of more ignoble animals ; for in all animals there 

 is something to admire because in all there is 

 the natural and the beautiful." He distinguished 

 five hundred species of mammals, birds, and fishes, 

 besides exhibiting an extensive knowledge of polyps, 

 sponges, cuttlefish, and other marine forms of life. 

 His four essays upon the parts, locomotion, genera- 

 tion, and vital principle of animals, show that he 

 fully understood Adaptation in its modern sense ; 

 he recognized the analogies if not the homologies 

 between different organs like the limbs ; he dis- 

 tinguished between the homogeneous tissues made 

 up of like parts and the heterogeneous organs 

 made up of unlike parts ; he perceived the under- 

 lying principle of physiological division of labour in 

 the different organs of the body ; he perceived the 

 unity of plan or type in certain classes of animals, 

 and considered rudimentary organs as tokens 

 whereby Nature sustains this unity; he rightly con- 

 ceived of life as the function of the organism, not as a 

 separate principle ; he anticipated Harvey's doctrine 



