Abstract: The enclosure includes a stationary panel having a depression formed in one of its faces. An opening is formed in the depression. A door is inset in the depression and it too is provided with an opening. The door reciprocates from an open position in which the two openings are side by side one another to a closed position in which the openings are no longer side by side. When the door is open, a passage is opened from outside the enclosure to its interior through which an animal may enter and depart from the enclosure. When the door is closed, so also is the passage.