Some years after our first experience with Pompilus scelestus we saw a wasp of this species carrying her spider home. She dropped it close to the nest, and looked meditatively, first at the hole and then at the spider. It was unquestionably going to be a very tight fit, but if she could get it in that would be an advantage; so after a moment she seized it by the tip of the abdomen and backing down tried to pull it after. Tug—_tug!_ No, it would not go down, and scelestus pushed it out and carried it to a place of safety up among some clover blossoms. She then washed and brushed herself neatly, and took several little walks, so that it was fully fifteen minutes before she began to enlarge her nest. All that time she must have carried in her little scrap of a mind the idea of doing a necessary act which was outside of her ordinary routine; and we noted with interest that the change when it was made accomplished exactly what was needed,—the spider went in, but not too easily. In an experiment with a French Sphex which has the habit of laying her cricket down at the threshold, and going inside for an instant before dragging it in, Fabre took advantage of the moment that the wasp was out of sight below to move her prey to a little distance, with the result that when the wasp came up she brought her cricket to the same spot and left it as before, while she visited the interior of the nest. Since he repeated this experiment about forty times and always with the same result, it seemed fair to draw the conclusion that nothing less than the performance of a certain series of acts in a certain order would satisfy her impulse. She must place her prey just so close to the doorway; she must then descend to examine the nest; and after that she must at once drag it down, any disturbance of this routine causing her to refuse to proceed. We once found a Sphex ichneumonea at work storing her nest, and thought it would be interesting to pursue Fabre’s method and find out whether she were equally persistent in following her regular routine. We allowed her to carry in one grasshopper to establish her normal method of procedure, and found that, bringing it on the wing, she dropped it about six inches away, ran into the nest, out again and over to the grasshopper, which she straddled and carried by the head to the entrance. She then ran down head first, turned around, came up, and seizing it by the head, pulled it within. On the following day, when she had brought a grasshopper to the entrance of the nest, and while she was below, we moved it back five or six inches. When she came out, she carried it to the same spot and went down as before. We removed it again, with the same result, and the performance was repeated a third and a fourth time, but the fifth time that she had found her prey where we had placed it she seized it by the head, and going backward dragged it down into the nest without pausing. On the next day the experiment was repeated.