Now, however desirable occasional closure may be, a permanent door would hamper the tarantula in her hunting operations, but the habits of the trap-door spider are different, and she closes her retreat with a wonderful hinged lid or “trap-door.” And the commonest form of trap-door is also the most perfect, being thick and tapering, and fitting accurately into the bevelled mouth of the tube like a stopper in the mouth of a bottle. It is made of alternate layers of spider silk and earth, and is free for more than half its circumference, the remaining portion of the surface disc being attached to the side of the tube by a flexible hinge of silk. Moggridge dissected the door of a full-sized tunnel into fourteen graduated discs. The smallest—and of course the lowest—represented the first door ever made by the spider, and the successively larger discs indicated the stages at which its increasing size rendered an enlargement of the tube—and therefore of the door—necessary. The spider always interweaves vegetable matter from the neighbourhood into each new disc, so that, as a rule, it is entirely indistinguishable from its surroundings when closed; and not only _dead_ vegetable matter, for if the tube is situated amongst moss, moss grows upon the lid. From our previous experience, however, we shall not be surprised to find that blind instinct and not forethought is responsible for this action. Moggridge removed the lid of a tunnel and also cleared the ground immediately round it of all vegetation; nevertheless, when the spider made a new door, it covered it with moss taken from the undisturbed vegetation beyond, so that the trap-door was now conspicuous as a green oasis in a sandy desert! And on another occasion a spider interwove fragments of scarlet fabric left purposely at hand into the lid of its tunnel. It is clear, therefore, that the decoration of the door is due to an instinct which impels the spider to utilise any material of the neighbourhood without any regard to the effect produced. The tube is densely lined with silk, which affords its architect a secure foot-hold, and if any enemy attempts to open the lid from without, the spider resists with all its strength—which is not inconsiderable—clinging on to its under surface with its front legs and jaws, while the claws of its other feet grasp the silken walls of the tube.