nergy, and store a certain quantity of it,
in the form of unused energy, in appropriate reservoirs, whence it could
be drawn at the desired moment, at the desired spot, in the desired
direction. The substances forming the food of animals are just such
reservoirs. Made of very complex molecules holding a considerable amount
of chemical energy in the potential state, they are like explosives
which only need a spark to set free the energy stored within them. Now,
it is probable that life tended at the beginning to compass at one and
the same time both the manufacture of the explosive and the explosion by
which it is utilized. In this case, the same organism that had directly
stored the energy of the solar radiation would have expended it in free
movements in space. And for that reason we must presume that the first
living beings sought on the one hand to accumulate, without ceasing,
energy borrowed from the sun, and on the other hand to expend it, in a
discontinuous and explosive way, in movements of locomotion. Even
to-day, perhaps, a chlorophyl-bearing Infusorian such as the Euglena may
symbolize this primordial tendency of life, though in a mean form,
incapable of evolving. Is the divergent development of the two kingdoms
related to what one may call the oblivion of each kingdom as regards one
of the two halves of the programme? Or rather, which is more likely, was
the very nature of the matter, that life found confronting it on our
planet, opposed to the possibility of the two tendencies evolving very
far together in the same organism? What is certain is that the vegetable
has trended principally in the first direction and the animal in the
second. But if, from the very first, in making the explosive, nature had
for object the explosion, then it is the evolution of the animal, rather
than that of the vegetable, that indicates, on the whole, the
fundamental direction of life.

The "harmony" of the two kingdoms, the complementary characters they
display, might then be due to the fact that they develop two tendencies
which at first were fused in one. The more the single original tendency
grows, the harder it finds it to keep united in the same living being
those two elements which in the rudimentary state implied each other.
Hence a parting in two, hence two divergent evolutions; hence also two
series of characters opposed in certain points, complementary in others,
but, whether opposed or complementary, always preserving