robably a protest against the sweeping
generalisations of his colleague, Etienne Geoffroy St Hilaire.

A true classification should be based upon the comparison of all
organs, but all organs are not of equal value for classification, nor
are all the variations of each organ equally important. In estimating
the value of variations more stress should be laid on function than on
form, for only those variations are important which affect the mode of
functioning. These are the principles on which Cuvier bases the
classification of animals given in the _Lecons_, Article V., "Division
des animaux d'apres l'ensemble de leur organisation." The scheme of
classification actually given in the _Lecons_ recalls curiously that
of Aristotle, for there is the same broad division into Vertebrates,
with red blood, and Invertebrates, almost all with white blood. Nine
classes altogether are distinguished--Mammals, Birds, Reptiles,
Fishes, Molluscs, Crustacea, Insects, Worms, Zoophytes (including
Echinoderms and Coelenterates).

A maturer theory and practice of classification is given in the _Regne
Animal_ of seventeen years later. Here the principle of the
subordination of characters (which seems to have been first explicitly
stated by the younger de Jussieu in his _Genera Plantarum_, 1789,[58])
is more clearly recognised. The properties or peculiarities of
structure which have the greatest number of relations of
incompatibility and coexistence, and therefore influence the whole in
the greatest degree, are the important or dominating characters, to
which the others must be subordinated in classification. These
dominant characters are also the most constant.[59] In deciding which
characters are the most important Cuvier makes use of his fundamental
classification of functions and organs into two main sets. "The heart
and the organs of circulation are a kind of centre for the vegetative
functions, as the brain and the spinal cord are for the animal
functions."[60] These two organ-systems vary in harmony, and their
characters must form the basis for the delimitation of the great
groups. Judged by this standard there are four principal types of
form,[61] of which all the others are but modifications. These four
types are Vertebrates, Molluscs, Articulates, and Radiates. The first
three have bilateral, the last has radial symmetry. Vertebrates and
Molluscs have blood-vessels, but Articulates show a functional
transition from the blood-vessel t