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 cocoon, 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 chemical 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 caterpillar; yet the whole of the foregoing must be thought out if a correct result 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, however, 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.