Abstract: An enclosure for animals of different sizes comprises two complementary shell housings that enclose an inner cage, which is slidably engaged to the shell housings by suitable fixtures such as track slides. In the fully closed position, the inner edges of the two shell housings meet, thereby forming a unitary enclosure. As the shell housings are drawn apart, a greater portion of the inner cage is exposed, thereby increasing the inner volume of the enclosure. In a second embodiment, the two housing shells are replaced with four partial shells that facilitate expansion in two directions.