ARISTOTLE'S CLASSIFICATION 5 



might, in addition to structural classifications, divide animals 

 into gregarious, solitary and social, or land animals into 

 troglodytes, surface-dwellers, and burrowers (Hist. Auiin., i.). 



He knew that dichotomous classifications were of little 

 use for animals (De Partibus, i. 3) and he explicitly and in so 

 many words accepted the principle of all " natural " classifica- 

 tion, that affinities must be judged by comparing not one but 

 the sum total of characters. As everyone knows, he was the 

 first to distinguish the big groups of animals, many of which 

 were already distinguished roughly by the common usages of 

 speech. Among his Sanguinea he did little more than define 

 with greater exactitude the limits of the groups established 

 by the popular classification. Among the " exsanguineous " 

 animals, however, corresponding to our Invertebrates, he 

 established a much more definite classification than the 

 popular, which is apt to call them indiscriminately " shellfish," 

 "insects," or "creeping things." He went beyond the 

 superficialities of popular classification, too, in clearly 

 separating Cetacea from fishes. He had some notion of 

 species and genera in our sense. He distinguished many 

 species of cuttlefish Octopus (Polypus] of which there were 

 many kinds, Eledone (Moschites) which he knew to have only 

 one row of suckers while Octopus has two, Argonauta, 

 Nautilus, Sepia, and apparently Loligo media (= his Teuthis) 

 and L. vulgaris (or forbesit] which seems to be his Teuthos. 

 He had a grasp of the principles which should be followed in 

 judging of the natural affinities of species. For example, he 

 knew that the cuckoo resembles .a hawk. " But," he says, 

 " the hawk has crooked talons, which the cuckoo has not, nor 

 does it resemble the hawk in the form of its head, but in 

 these respects is more like the pigeon than the hawk, which 

 it resembles in nothing but its colour; the markings, 

 however, upon the hawk are like lines, while the cuckoo is 

 spotted" (Hist. Anint., Cresswell's trans., p. 147, London, 

 1862). 



The groups he distinguished were man, viviparous 

 quadrupeds, oviparous quadrupeds, birds, fishes, Cetacea, 

 Cephalopoda, Malacostraca ( = higher Crustacea), Insecta 

 ( = annulose animals), Testacea ( = molluscs, echinoderms, 

 ascidians). A class of Acalephae, including sea-anemones and 



