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mal being as successful as its later ones. There is a difference in princi-
ple here which cannot be mistaken. Again, we know by experience that
the feebler and more limited an intelligence is, the more slowly do ideas
act upon it, that is to say, the slower and more laborious is its conscious
thought. So long as instinct does not come into play, this holds good
both in the case of men of different powers of comprehension and with
animals; but with instinct all is changed, for it is the speciality of instinct
never to hesitate or loiter, but to take action instantly upon perceiving
that the stimulating motive has made its appearance. This rapidity in ar-
riving at a resolution is common to the instinctive actions both of the
highest and the lowest animals, and indicates an essential difference be-
tween instinct and conscious deliberation.
Finally, as regards perfection of the power of execution, a glance will
suffice to show the disproportion that exists between this and the grade
of intellectual activity on which an animal may be standing. Take, for
instance, the caterpillar of the emperor moth (Saturnia pavonia minor).
It eats the leaves of the bush upon which it was born; at the utmost has
just enough sense to get on to the lower sides of the leaves if it begins to
rain, and from time to time changes its skin. This is its whole existence,
which certainly does not lead us to expect a display of any, even the
most limited, intellectual power. When, however, the time comes for the
larva of this moth to become a chrysalis, it spins for itself a double co-
coon, fortified with bristles that point outwards, so that it can be opened
easily from within, though it is sufficiently impenetrable from without.
If this contrivance were the result of conscious reflection, we should
have to suppose some such reasoning process as the following to take
place in the mind of the caterpillar:- I am about to become a chrysalis,
and, motionless as I must be, shall be exposed to many different kinds of
attack. I must therefore weave myself a web. But when I am a moth I
shall not be able, as some moths are, to find my way out of it by chemi-
cal or mechanical means; therefore I must leave a way open for myself.
In order, however, that my enemies may not take advantage of this, I will
close it with elastic bristles, which I can easily push asunder from
within, but which, upon the principle of the arch, will resist all pressure
from without. Surely this is asking rather too much from a poor cater-
pillar; yet the whole of the foregoing must be thought out if a correct re-
sult is to be arrived at.
This theoretical separation of instinct from conscious intelligence can be
easily misrepresented by opponents of my theory, as though a separation
in practice also would be necessitated in consequence. This is by no
means my intention. On the contrary, I have already insisted at some
length that both the two kinds of mental activity may co-exist in all
manner of different proportions, so that there may be every degree of
combination, from pure instinct to pure deliberation. We shall see, how-
ever, in a later chapter, that even in the highest and most abstract activity
of human consciousness there are forces at work that are of the highest
importance, and are essentially of the same kind as instinct.
On the other hand, the most marvellous displays of instinct are to be
found not only in plants, but also in those lowest organisms of the sim-
plest bodily form which are partly unicellular, and in respect of con-
scious intelligence stand far below the higher plants - to which, indeed,
any kind of deliberative faculty is commonly denied. Even in the case
of those minute microscopic organisms that baffle our attempts to clas-
sify them either as animals or vegetables, we are still compelled to ad-
mire an instinctive, purposive behaviour, which goes far beyond a mere
reflex responsive to a stimulus from without; all doubt, therefore, con-
cerning the actual existence of an instinct must be at an end, and the at-
tempt to deduce it as a consequence of conscious deliberation be given
up as hopeless. I will here adduce an instance as extraordinary as any
we yet know of, showing, as it does, that many different purposes, which
in the case of the higher animals require a complicated system of organs
of motion, can be attained with incredibly simple means.
Arcella vulgaris is a minute morsel of protoplasm, which lives in a
concave-convex, brown, finely reticulated shell, through a circular open-
ing in the concave side of which it can project itself by throwing out
pseudopodia. If we look through the microscope at a drop of water con-
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