f complexity in the nervous system. No doubt, each complication of any
part of the organism involves many others in addition, because this part
itself must live, and every change in one point of the body
reverberates, as it were, throughout. The complication may therefore go
on to infinity in all directions; but it is the complication of the
nervous system which conditions the others in right, if not always in
fact. Now, in what does the progress of the nervous system itself
consist? In a simultaneous development of automatic activity and of
voluntary activity, the first furnishing the second with an appropriate
instrument. Thus, in an organism such as ours, a considerable number of
motor mechanisms are set up in the medulla and in the spinal cord,
awaiting only a signal to release the corresponding act: the will is
employed, in some cases, in setting up the mechanism itself, and in the
others in choosing the mechanisms to be released, the manner of
combining them and the moment of releasing them. The will of an animal
is the more effective and the more intense, the greater the number of
the mechanisms it can choose from, the more complicated the switchboard
on which all the motor paths cross, or, in other words, the more
developed its brain. Thus, the progress of the nervous system assures to
the act increasing precision, increasing variety, increasing efficiency
and independence. The organism behaves more and more like a machine for
action, which reconstructs itself entirely for every new act, as if it
were made of india-rubber and could, at any moment, change the shape of
all its parts. But, prior to the nervous system, prior even to the
organism properly so called, already in the undifferentiated mass of the
amoeba, this essential property of animal life is found. The amoeba
deforms itself in varying directions; its entire mass does what the
differentiation of parts will localize in a sensori-motor system in the
developed animal. Doing it only in a rudimentary manner, it is dispensed
from the complexity of the higher organisms; there is no need here of
the auxiliary elements that pass on to motor elements the energy to
expend; the animal moves as a whole, and, as a whole also, procures
energy by means of the organic substances it assimilates. Thus, whether
low or high in the animal scale, we always find that animal life
consists (1) in procuring a provision of energy; (2) in expending it, by
means of a matter as suppl