inguished two.

(2) Aristotle had various systems of classifying animals. They could
be classified, he thought, according to their structure, their manner
of reproduction, their manner of life, their mode of locomotion, their
food, and so on. Thus you might, in addition to structural
classifications, divide animals into gregarious, solitary and social,
or land animals into troglodytes, surface-dwellers, and burrowers
(_Hist. Anim._, 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" classification, 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
_forbesii_) 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. Anim._,
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 (= a