Form and Function | Page 3

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;
second, the first scientific classification of animals;[6] third, a clear
enunciation of the fact of community of plan within each of the big

groups; fourth, an attempt to explain certain instances of the correlation
of parts; fifth, a pregnant distinction between homogeneous and
heterogeneous parts; sixth, a generalisation on the succession of forms
in development; and seventh, the first enunciation of the idea of the
Échelle des êtres.
(1) What surprises the modern reader of the Historia Animalium
perhaps more than anything else is the extent and variety of Aristotle's
knowledge of animals. He describes more than 500 kinds.[7] Not only
does he know the ordinary beasts, birds, and fishes with which
everyone is acquainted, but he knows a great deal about cuttlefish,
snails and oysters, about crabs, crawfish (Palinurus), lobsters, shrimps,
and hermit crabs, about sea-urchins and starfish, sea-anemones and
sponges, about ascidians (which seem to have puzzled him not a little!).
He has noticed even fish-lice and intestinal worms, both flat and round.
Of the smaller land animals, he knows a great many insects and their
larvæ. The extent of his anatomical knowledge is equally surprising,
and much of it is clearly the result of personal observation. No one can
read his account of the internal anatomy of the chameleon (Hist. Anim.,
ii.), or his description of the structure of cuttlefish (Hist. Anim., iv), or
that touch in the description of the hermit crab (Hist. Anim., iv.)--" Two
large eyes ... not ... turned on one side like those of crabs, but straight
forward"--without being convinced that Aristotle is speaking of what
he has seen. Naturally he could not make much of the anatomy of small
insects and snails, and, to tell the truth, he does not seem to have cared
greatly about the minutiæ of structure. He was too much of a Greek and
an aristocrat to care about laborious detail.
Not only did he lay a foundation for comparative anatomy, but he made
a real start with comparative embryology. Medical men before him had
known many facts about human development; Aristotle seems to have
been the first to study in any detail the development of the chick. He
describes this as it appears to the naked eye, the position of the embryo
on the yolk, the palpitating spot at the third day, the formation of the
body and of the large sightless eyes, the veins on the yolk, the
embryonic membranes, of which he distinguished 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.