ed in various ways. The processes of regeneration, for
instance, are compared with the similar tendencies observed in crystals,
which when they are injured have the capacity of restoring their normal
form. This capacity therefore obtains in the realm of the inorganic as
well as among organisms, and is referred to the tendency of all substances
to maintain a definite state of equilibrium, conditioned by their form,
and, if that is disturbed, to return to a similar or a new state of
equilibrium. Or, the procedure may be to reduce the processes of a
developmental or morphogenetic category to processes of stimulation in
general, and then it is believed, or even demonstrated, that
chemo-physical analogies or explanations can be found for them.

Thus, for instance, it is shown that the egg of the sea-urchin may be
"stimulated" to development, not exclusively by the fertilising sperm, but
even by a simple chemical agent, or that spermatozoids which are seeking
the ovum to be fertilised may be attracted by malic acid. These are
"reductions" of the higher phenomena of life to the terms of a lower and
simpler process of "stimulus," that is to say, to chemotropism in the
second case and something analogous in the first. A further reduction
would be to show that the movement of the spermatozoids towards the malic
acid is not a "vitalistic" act, much less a psychically conditioned one,
(that is, conditioned by "taste," "sensation," and the voluntary or
instinctive impulse liberated thereby), but is a chemo-physical process,
although perhaps an exceedingly complex one. It would be another
"reduction" of this second kind, if, for instance, the well-known effect
of light on plants, which makes them turn their leaves towards it
(heliotropism), could be shown to be due to more rapid growth of the leaf
on the shaded side, which would lift up the leaf and cause it to turn, or
to an increase of turgescence on the shaded side, and if it could be shown
that the increase in either case was a simple and obvious physical
process, the necessary consequence of the decreased amount of light.

It is obvious, and it is also thoroughly justifiable, that all attempts
along these lines of interpretation should be undertaken in the first
place in connection with the simplest and lowest forms of life. It is in
the investigation of the "Protists," the study of the vital phenomena of
the microscopically minute unicellular organisms, that attempts of this
ki