e, like fine hairs, which beat the water as
oars do. Some of them have one strong oar, like the gondolier (but in
front of the boat); others have two or more oars; while some have their
little flanks bristling with fine lashes, like the flanks of a Roman
galley.

If we imagine this simple principle at work for ages among the primitive
microbes, we understand the first great division of the living world,
into plants and animals. There must have been a long series of earlier
stages below the plant and animal. In fact, some writers insist that the
first organisms were animal in nature, feeding on the more elementary
stages of living matter. At last one type develops chlorophyll (the
green matter in leaves), and is able to build up plasm out of inorganic
matter; another type develops mobility, and becomes a parasite on the
plant world. There is no rigid distinction of the two worlds. Many
microscopic plants move about just as animals do, and many animals live
on fixed stalks; while many plants feed on organic matter. There is so
little "difference of nature" between the plant and the animal that the
experts differ in classifying some of these minute creatures. In fact,
we shall often find plants and animals crossing the line of division. We
shall find animals rooting themselves to the floor, like plants, though
they will generally develop arms or streamers for bringing the food to
them; and we shall find plants becoming insect-catchers. All this
merely shows that the difference is a natural tendency, which special
circumstances may overrule. It remains true that the great division
of the organic world is due to a simple principle of development;
difference of diet leads to difference of mobility.

But this simple principle will have further consequences of a most
important character. It will lead to the development of mind in one half
of living nature and leave it undeveloped in the other. Mind, as we know
it in the lower levels of life, is not confined to the animal at
all. Many even of the higher plants are very delicately sensitive
to stimulation, and at the lowest level many plants behave just like
animals. In other words, this sensitiveness to stimuli, which is
the first form of mind, is distributed according to mobility. To the
motionless organism it is no advantage; to the pursuing and pursued
organism it is an immense advantage, and is one of the chief qualities
for natural selection to foster.

For the moment, h