Long before it works up to man we see this amazing force stemming an uncountable number of attacks, and meeting ruinous conditions with daring contrivances. For one kind of danger it develops a shell, for another a sting, for another a poison, for another a protective colouration. To breathe in the sea it puts forth gills, and makes lungs for itself when stranded on the land. In glacial cold it finds the means of growing fur; when heat and cold assail it by turns it packs itself with feathers; when climates become temperate it produces hair. For the creature which keeps to the water it webs the foot; for that which takes to the trees it makes the toes prehensile; for the one which learns to stand erect and run along the ground it flattens the sole, making it steady and supporting. To resist, to survive, to win through, is the end to which the life-principle sets itself with such singleness of aim as to unfold a wealth of potentiality astounding to us in looking backward. VIII This was the idea which came back to me that autumn at Versailles, and from which in the course of time I drew my conclusions. Briefly, those conclusions were to the effect that as individuals we need difficulties to overcome, and that fear is a stimulus to overcoming them. Otherwise expressed, fear loses much of its fearfulness when we see it as the summons to putting forth new energies. Unless we were conscious of the energies such a call would not reach us. The creatures preceding man could have felt no misgiving, since they lacked the imagination essential to a dread. Such fear as they were equal to must have seized them in paroxysms of terror when calamities threatened to overwhelm them. If they made good their escape no trace of the fear remained behind, the brain having little or no power of retention. We may take it for granted that the pterodactyl and the trachodon had none of the foreboding based on experience which destroys the peace of man. Fear, as we understand it, was in itself a signal of advance. It could only have begun with the exercise of reason. Arrived at the rudiments of memory the creature must have been able to perceive, however dimly, that the thing which had happened might happen again. Adding the first stirrings of imagination he must have constructed possible events in which the danger would come from the same causes as before. With the faculties to remember, to reason, and to imagine all at work we reach the first stages of man.