The book is available at Project Gutenberg, Internet Archive, Baldwin Project, Hathi Trust, and Google Books. There is also a free audiobook at LibriVox.
There are different illustrated editions; this Internet Archive edition has illustrations by Joseph M. Gleeson, and I have made a Flickr collection.
How the Camel Got His Hump
How the Rhinoceros Got His Skin
How the Leopard Got His Spots
The Elephant's Child
The Sing-Song of Old Man Kangaroo
The Beginning of the Armadillos
How the First Letter was Written
How the Alphabet was Made
The Crab that Played with the Sea
The Cat that Walked by Himself
The Butterfly that Stamped
