CLASSICAL ANTIQUITY, MIDDLE AGES 39 



a number of systematic categories. "Animals may be characterized accord- 

 ing to their way of living, their actions, their habits, and their bodily parts. ' ' 

 According to the three first-named principles they are divided into land- 

 animals and aquatic animals; certain of the latter live entirely i.'i the water — 

 the fishes; others live most of their time there, but breathe and breed outside 

 it — otters, beavers, crocodiles. The water-animals can partly swim, partly 

 creep, and in part they are adherent. The land-animals have similar charac- 

 teristics as regards habitat and way of living, feeding, habits, and character. 

 The most important bases of classification, however, are the parts of ani- 

 mals' bodies, both external and internal: motive organs, respiration, organs 

 of sense, blood-circulation. By combining various qualities the groups are 

 defined and characterized. These groups are variously extensive: "Many 

 animals allow of association into large divisions, such as birds, fishes, and 

 whales," and, further, ink-fish, shell-fish or mussels, and crayfi:li. Others 

 are more difficult to classify, such as the quadrupeds, which may certainly be 

 classified as oviparous and viviparous, but amongst these it is not possible 

 to make subdivisions, the animals having to be characterized each separately. 

 The categories which Aristotle thus established he never summarized; his 

 tabulated and generally recognized "system" has been extracted from his 

 writings by others and need not be repeated here, all the more so as it is 

 reproduced in different ways by different authors. Otherwise, his systematic 

 categories are only two in number, the genos and the eidos, the latter corre- 

 sponding to the individual animal form — horse, dog, lion — the former to 

 all combinations of a higher degree. That is really the reason why his sys- 

 tem cannot be compared with the Linnxan, with its manifold categories, 

 though it by no means detracts from its pioneer importance for all time. 



His knoivledge of forms 

 In connexion with the system of Aristotle a few words may be said about 

 his knowledge of form — about the material out of which he built up his 

 system. In his writings have been recognized about 5x0 of the species which 

 present-day zoology has classified. These forms all belong to Greece and its 

 seas, and it seems that marine fauna interested him more almost than land 

 fauna; fishes, molluscs, and crustaceans are better represented in his works 

 than land-animals — in sharp contrast to what was afterwards the case with 

 Linnasus. Exotic animals Aristotle knows only from the descriptions of 

 others; it has often been stated that Alexander used to send him material for 

 investigation from the countries he conquered, but this can hardly be true. 

 The crocodile, for instance, he describes in the exact words of Herodotus 

 and he accepts as true without further comment the latter's statement that 

 the upper jaw of that creature is jointed on the lower jaw — which he would 

 never have said had he seen a crocodile. Still more remarkable is the fact 

 that he apparently never saw, or at any rate never carefully examined, a 



