Are the two guided by memory when placed by man beyond their bearings and carried to great distances—into regions with which they are unacquainted and in unknown directions? Is memory as quick when, having reached a certain height at which they can in some sort take their bearings, they launch themselves with all their power of wing towards that part of the horizon where are their nests? Is it memory which traces their aerial way across regions seen for the first time? Evidently not. It is not possible to recollect the unknown. The Hymenopteron and the bird know nothing of their surroundings; nothing can have taught them the general direction which they followed when carried thither, for it was in the darkness of a closed box that the journey was made. Locality, orientation,—all is unknown, and yet they find their way. They have then as guide something better than simple memory—a special faculty, a kind of topographic consciousness of which we can form no idea, possessing nothing analogous to it. I am now about to establish experimentally how subtle and precise is this faculty in the narrow cycle where it is applied, and also how limited and obtuse when it has to move out of habitual conditions. Such is the invariable antithesis of instinct. A Bembex, actively engaged in feeding her larva, has left her burrow. She will return immediately with the product of the chase. The entrance is carefully stopped with sand—swept backward by the insect before departing. Nothing distinguishes it from the rest of the sandy surface. But this offers no difficulty to the Hymenopteron, who finds her doorway again with a sagacity which I have already described. Let us plan some treachery; let us perplex her by altering the state of the place. I cover the entrance with a flat stone as large as my hand. She soon returns. The complete change made upon her threshold during her absence does not seem to cause her the slightest hesitation; at all events she alights immediately upon the stone, and tries for an instant to hollow it, not at a chance spot, but exactly over the opening of her burrow. Quickly turned aside from this attempt by the hardness of the obstacle, she traverses the stone in every direction, goes round it, slips underneath, and begins to dig in the precise direction of her dwelling.