he end of which it will accomplish infinitely
varied kinds of work. That is what the _vital impetus_, passing through
matter, would fain do all at once. It would succeed, no doubt, if its
power were unlimited, or if some reinforcement could come to it from
without. But the impetus is finite, and it has been given once for all.
It cannot overcome all obstacles. The movement it starts is sometimes
turned aside, sometimes divided, always opposed; and the evolution of
the organized world is the unrolling of this conflict. The first great
scission that had to be effected was that of the two kingdoms, vegetable
and animal, which thus happen to be mutually complementary, without,
however, any agreement having been made between them. To this scission
there succeeded many others. Hence the diverging lines of evolution, at
least what is essential in them. But we must take into account
retrogressions, arrests, accidents of every kind. And we must remember,
above all, that each species behaves as if the general movement of life
stopped at it instead of passing through it. It thinks only of itself,
it lives only for itself. Hence the numberless struggles that we behold
in nature. Hence a discord, striking and terrible, but for which the
original principle of life must not be held responsible.

It is therefore conceivable that life might have assumed a totally
different outward appearance and designed forms very different from
those we know. With another chemical substratum, in other physical
conditions, the impulsion would have remained the same, but it would
have split up very differently in course of progress; and the whole
would have traveled another road--whether shorter or longer who can
tell? In any case, in the entire series of living beings no term would
have been what it now is.

There are numerous cases in which nature seems to hesitate between the
two forms, and to ask herself if she shall make a society or an
individual. The slightest push is enough, then, to make the balance
weigh on one side or the other. If we take an infusorian sufficiently
large, such as the Stentor, and cut it into two halves each containing a
part of the nucleus, each of the two halves will generate an independent
Stentor; but if we divide it incompletely, so that a protoplasmic
communication is left between the two halves, we shall see them execute,
each from its side, corresponding movements; so that in this case it is
enough that a thread shou