often repeated, just like the winding-up of a watch, which is often done at a wrong time, for instance, on changing clothes during the day, and thus without reflection. It is quite easy to conceive that if the material brain-adaptation which causes flight without reflection at the sight of man were transmissible, the flight-instinct might become a congenital instinct in the species in question. But this assumption is unfounded; for, as is shown by the case of the sea-cow, we do not require it where the animal is of sufficient intelligence to perform by its own discernment the action necessary to its existence. The action may thus become 'instinctive' through exercise and imitation in the _individual_ life, without however attaining to transmissibility. But in many cases this is not enough, namely, in all cases in which the degree of intelligence is not sufficiently high, or where the flight movement must follow so rapidly that it would be too late if it had to be regulated by the will, as, for instance, the shutting of the lids when the eye is threatened, or the flight of the fly or the butterfly when an enemy approaches. Both fly and butterfly would be lost in every case if they had voluntarily to set the flight-movement going after they became conscious of danger. If they had first of all to find out from whom danger threatened no individual would escape an early death, and the species would die out. But they possess an instinct which impels them to fly up with lightning speed, and in an opposite direction, whenever they have a visual perception of the rapid approach of any object of whatever nature. For this reason they are difficult to catch. I once watched the play of a cat, ordinarily very clever at catching, as she attempted to seize a peacock-butterfly (_Vanessa Io_), which settled several times on the ground in front of her. Quietly and slowly she crept within springing distance, but even during the spring the butterfly flew up just before her nose and escaped every time, and the cat gave it up after three attempts.