At last the Bembex arrives and makes straight for her absent door, only the threshold of which remains. There for a good hour did I see her dig, sweep the surface, send the sand flying, and persist, not in making a new gallery, but in seeking the loose sand barrier which should yield to the mere pressure of her head and let her pass easily. Instead of loose materials she finds firm soil not yet disturbed. Warned by this resistance she limits her efforts to exploring the surface, always close to where the door should be, only allowing herself to deviate a few inches. She returns to sound and sweep places already sounded and swept some twenty times, unable to leave her narrow circle, so obstinately convinced is she that the door must be there and nowhere else. With a straw I pushed her gently and repeatedly to another point. She would have none of it, and came back at once to where the door ought to have been. Now and then the gallery, turned into a semi-canal, appeared to attract her attention, but very faintly. She would go a few steps along it, still raking, and then return to the entrance. Two or three times I saw her go the whole length of the gallery and reach the cul-de-sac where the larva should be, do a little careless raking, and hurry back where the entrance used to be, and continue searching with a patience which exhausted mine. More than an hour had passed, and still she sought on the site whence the door had disappeared. What would happen in the presence of the larva? That was the second part of the question. To continue the experiment with the same Bembex would not have offered sufficient guarantee, as the creature, rendered more obstinate by her vain search, seemed possessed by a fixed idea, and this would have interfered with the facts which I wanted to prove. I required a new subject, concerned solely with the impulses of the actual moment. An opportunity soon came. The burrow was uncovered, as I have just said; but I did not touch the contents; larva and food were left in their places,—all was in order inside, the roof only was wanting. Well, with this open dwelling, whose every detail the eye could embrace,—vestibule, gallery, cell at the far end, with the grub and its heap of provender,—this dwelling turned into a roofless gallery at the end of which the larva was moving restlessly, under the hot sun, its mother continued the manœuvres already described. She alighted just where the entrance had been, and there it was that she hunted about and swept the sand—there that she always returned after some hasty attempt elsewhere in a circuit of a few inches. No exploration of the gallery—no anxiety for the distressed larva; though the grub, whose delicate skin has just exchanged the gentle moisture of a cave for burning sunshine, is writhing on its heap of chewed Diptera, the mother takes no notice of it. For her it is no more than any one of the objects strewn on the sand,—a little pebble, a clod, a scrap of dried