Let us return to the Pelopæus, to whom it is time to apply the experimental method. A cell has recently been completed. The huntress arrives with her first Spider. She stores it away and at once fastens her egg upon the Spider’s belly. She sets out on a second trip. I take advantage of her absence to remove with my tweezers from the bottom of the cell the head of game and the egg. What will the insect do on its return, confronted with this empty cell, this cell no longer containing the egg, the sole object of her industry as a potter and her skill as a huntress? The disappearance of the egg must be obvious to the Wasp who has been robbed of it, if her poor intelligence possess so much as the rudimentary gleam that enables us to distinguish between a thing’s presence and its absence. The egg, were it alone, being of small dimensions, might escape the mother’s vigilance; but it lies upon a comparatively bulky Spider, of whose presence the Pelopæus, on returning to the nest, is undoubtedly apprised by her sense of touch and sight when she deposits the second victim beside the first. If this big object be missing, the egg is missing likewise, so the most elementary trace of reason that it is possible to conceive ought to tell her. Once more, what will the Pelopæus do when confronted with her cell, where the absence of the egg henceforth renders the bringing of provisions useless and absurd, unless and until she repairs the loss by laying a second egg? She will do precisely what we have already seen in the Mason-bee of the Sheds, but under less striking conditions: she will act absurdly and wear herself out uselessly. What she does is to bring a second Spider, whom she stores away with the same cheerful zeal as though nothing untoward had occurred; she brings a third, a fourth and others still, each of whom I remove during her absence, so that every time that she returns from the chase the warehouse is found empty. For two days the Pelopæus’ obstinacy in seeking to fill the insatiable jar persisted; for two days my patience in emptying the pot as she stocked it was equally unflagging. With the twentieth victim, persuaded, perhaps, by the fatigue of expeditions repeated beyond all measure, the huntress considered that the game-bag was sufficiently supplied; and she began most conscientiously to close the cell which contained absolutely nothing.