ms of "pure morphology," but because he described the structure
of many animals and classified them in a scientific way. We shall
discuss here the morphological ideas which occur in his writings upon
animals--in the _Historia Animialium_, the _De Partibus Animalium_,
and the _De Generatione Animalium_.

The _Historia Animalium_ is a most comprehensive work, in some ways
the finest text-book of Zoology ever written. Certainly few modern
text-books take such a broad and sane view of living creatures.
Aristotle never forgets that form and structure are but one of the
many properties of living things; he takes quite as much interest in
their behaviour, their ecology, distribution, comparative physiology.
He takes a special interest in the comparative physiology of
reproduction. The _Historia Animalium_ contains a description of the
form and structure of man and of as many animals as Aristotle was
acquainted with--and he was acquainted with an astonishingly large
number. The later _De Partibus Animalium_ is a treatise on the causes
of the form and structure of animals. Owing to the importance which
Aristotle ascribed to the final cause this work became really a
treatise on the functions of the parts, a discussion of the problems
of the relation of form to function, and the adaptedness of structure.

Aristotle was quite well aware that each of the big groups of animals
was built upon one plan of structure, which showed endless variations
"in excess and defect" in the different members of the group. But he
did not realise that this fact of community of plan constituted a
problem in itself. His interest was turned towards the functional side
of living things, form was for him a secondary result of function.

Yet he was not unaware of facts of form for which he could not quite
find a place in his theory of organic form, facts of form which were
not, at first sight at least, facts of function. Thus he was aware of
certain facts of "correlation," which could not be explained off-hand
as due to correlation of the functions of the parts. He knew, for
instance, that all animals without front teeth in the upper jaw have
cotyledons, while most that have front teeth on both jaws and no horns
have no cotyledons (_De Gen._, ii. 7).

Speaking generally, however, we find in Aristotle no purely
morphological concepts. What then does morphology owe to Aristotle? It
owes to him, _first_, a great mass of facts about the structure of
animals