Collects Uncanny X-Men (1963) #455-461. High adventure in the Savage Land! The X-Men discover a wondrous and advanced new civilization when they return to the isolated, Antarctic jungle - but it's none-too-friendly toward humans. . . or mutants! And could the X-Men have unintentionally helped them take their first steps toward world domination? Plus: The team gains a highly unexpected new member!