The story of his own connection with the cabin had never been told him. The language of the apes had so few words that they could talk but little of what they had seen in the cabin, having no words to accurately describe either the strange people or their belongings, and so, long before Tarzan was old enough to understand, the subject had been forgotten by the tribe.
Only in a dim, vague way had Kala explained to him that his father had been a strange white ape, but he did not know that Kala was not his own mother.

Ch. 6 : Jungle Battles - Tarzan of the Apes (1912)