s to reduce development to its "simple
components," but its main task at the present day and for many years to
come is the analysis of development into its "complex components."

These complex components must be accepted as having much of the validity
of physical and chemical laws. They are mysterious in the sense that
they cannot yet be explained mechanistically, but they are constant in
their action, and under the same conditions produce always the same
effect--hence they may be made the subject of strictly scientific study.
They represent biological generalisations, in their way of equal
validity with the generalisations of physics and chemistry.

The principal "complex components" which Roux recognises are somewhat as
follows:--First come the elementary cell-functions of assimilation and
dissimilation, growth, reproduction and heredity, movement and
self-division (as a special co-ordination of cell-movements). Then at a
somewhat higher level, self-differentiation, and the trophic reaction to
functional stimuli. Components of even greater complexity may also be
distinguished, as, for instance, the biogenetic law. The various
tropisms exhibited in development may be regarded as "directive" complex
components. There must be added, not as being itself a component, but
rather as a mode or peculiar property of all functioning, the
omnipresent faculty of self-regulation.

It will be noticed that Roux's "complex components" are simply the
general properties or functions of organised matter.

Expressing Roux's thought in another way, we might say that life can
only be defined functionally, _i.e._, by an enumeration of the "complex
components" or elementary functions which all living beings manifest,
even down to the very simplest. "Living beings," writes Roux, "can at
present be defined with any approach to completeness only functionally,
that is to say, through characterisation of their activities, for we
have an adequate acquaintance with their functions in a general way,
though our knowledge of particulars is by no means complete" (p. 105,
1905). Defined in the most general and abstract way, living things are
material objects which persist in spite of their metabolism, and, by
reason of their power of self-regulation, in spite also of the changes
of the environment. This is the "functional minimum-definition of life"
(pp. 106-7, 1905).

We may now go on to consider the relation of function to form throughout
the cour