Useful acts habitually repeated may become invincible, like veritable instinctive movements. A hunter[1] spending the winter in an isolated cabin in Canada engaged an Indian woman to keep house for him. She arrives in the evening, melts the snow, begins to wash up, shifts everything, prevents his getting any sleep. He rages. Silence. As soon as he is asleep, the woman mechanically begins to work again, and so on, until the humble Indian gets the last word. Here, exactly as among insects, one has the example of work which once begun must go on until it is finished. The insect can not be interrupted; if it is interrupted by external cause it starts work again not at the point where it actually finds the work, but at the point where it, the insect, left off. Thus, one entirely removed the nest which a chalicodome was building on a shingle; the bee returns, finds nothing, since there is nothing to find, but instead of recommencing the building, continues it. There was nothing to be done but close the hole; the bee closes it, that is to say she deposits the last mouthful of mortar on the ideal dome of an absent nest: then with instinct satisfied, sure of having assured her posterity, she retires, she goes to die. One can get the same result with the pélopée, and with other builders. Processional caterpillars are accustomed to make long trips in Indian file on the branches of their native pine-tree, in search of food: if one place them on the rim of a basin they will stupidly circulate for thirty hours, without one of them having the idea of interrupting the circle by going off at a tangent. They will die in their track, stuck fast in obedience; when one falls another steps into his place, the ranks close, that is all. Here are the extremities of instinct, and to our great surprise they are almost the same in an Indian of the great lakes and in a processional pine caterpillar.