The film opens with men wearing ape suits with their huge cocks hanging free.
The movie does not start until the boy-ape is preparing for the ape tribes rites of manhood. He was raised tenderly by the women in the tribe and has been snatched away by the older males of the tribe to suffer him to the rites of the tribe.
When the tribe makes its morning raid on a neighboring group of apes it is particularly savage to see the boy ape use a scooper blade to make up for his fairly small digits. He often has developed and used tools to compensate for his various weaknesses. This is one of the reasons from an early age he was able to use his penis as a tail. He swings from his now prehensile penis tearing the skins off the victims with astonishing speed. The scene is so horrible his own tribe is a little wigged on him now.
Jealous of the tittering laughter of all the women. The big joke in the tribe about how scrawny Tarzan has a penis that is like a tail. The women apes when they are sitting and grooming chids the men of the tribe that if they had a penis that was a tail they could be proud. To have their pride injured by this scrawny weak overgrown ape-boy was too much.
Tarzan had to go.