Indeed, an octopus is amazing, as this survey of its habits and life cycle amply proves: it not only conceals itself with obfuscating ink but can change color; it also demonstrates surprising intelligence. Keller's simple illustrations convey a clear sense of this fascinating invertebrate and its environment. Pitched to somewhat older readers, How We Learned the Earth is Round is a historical overview of a question that intrigues every curious child. The text here (though it doesn't explain how the Greeks knew that the moon shone with reflected light) is stronger than the illustrations, which, though attractive, add more confusion than clarification to the reason for the moon's phases. Nonetheless, two useful, lucidly written introductions.