neral laws which are as certain as those which are derived from
calculation or from experiment."[46]

By "conditions of existence" he means something quite different from
what is now commonly understood. The idea of the external conditions
of existence, the environment, enters very little into his thought. He
is intent on the adaptations of function and organ within the living
creature--a point of view rather neglected nowadays, but essential for
the understanding of living things. The very condition of existence of
a living thing, and part of the essential definition of it, is that
its parts work together for the good of the whole.

The principle of the adaptedness of parts may be used as an
explanatory principle, enabling the naturalist to trace out in detail
the interdependence of functions and their organs. When you have
discovered how one organ is adapted to another and to the whole, you
have gone a certain way towards understanding it. That is using
teleology as a regulative principle, in Kant's sense of the word.
Cuvier was indeed a teleologist after the fashion of Kant, and there
can be no doubt that he was influenced, at least in the exposition of
his ideas, by Kant's _Kritik der Urtheilskraft_, which appeared ten
years before the publication of the _Lecons d'Anatomie Comparee_.
Teleology in Kant's sense is and will always be a necessary postulate
of biology. It does not supply an explanation of organic forms and
activities, but without it one cannot even begin to understand living
things. Adaptedness is the most general fact of life, and innumerable
lesser facts can be grouped as particular cases of it, can be, so far,
understood.

Cuvier's famous principle of correlation, the corner-stone of his
work, is simply the practical application to the facts of structure of
the principle of functional adaptedness. By the principle of
correlation, from one part of an animal, given sufficient knowledge of
the structure of its like, you can in a general way construct the
whole. "This must necessarily be so: for all the organs of an animal
form a single system, the parts of which hang together, and act and
re-act upon one another; and no modifications can appear in one part
without bringing about corresponding modifications in all the
rest."[47] The logical basis of the principle is sound. The functions
of the parts are all intimately bound up with one another, and one
function cannot vary without bringing in its train