His little face was tense in study, for he had partially grasped, in a hazy, nebulous way, the rudiments of a thought which was destined to prove the key and the solution to the puzzling problem of the strange little bugs.
In his hands was a primer opened at a picture of a little ape similar to himself, but covered, except for hands and face, with strange, colored fur, for such he thought the jacket and trousers to be. Beneath the picture were three little bugs — BOY.

Ch. 7 : The Light of Knowledge - Tarzan of the Apes (1912)