Getting near to the end of the book, not good, not bad, I prefer Tarzan, Lord of the Jungle, the only other Tarzan book I ever read.
One detail I'm gonna mention. The novel (published in 1933) features a mad scientist, who discovers how traits are inherited, genes and such, and he figures out he can implant stem cells from one specimen to another and give the traits of the first to the second one. It can be done within species and he creates speaking and thinking gorillas and a society out of them resembling to 16th century England.
But this scientists go even further solving immortality. Well, at least his. He realizes consuming stem cells can revitalize the body, and for while he survives on the children of his ape society.
This story very much reminds me of something...