What about Gorilla sexuality?
Gorillas have no mating season. Mating and births occur throughout the year. Female gorillas have a hormone cycle (similar to humans), which is usually 26-32 days long.
The female comes into heat in mid-cycle. This can last up to 4 days, but usually it lasts only one day. During this phase the female's behaviour and the relations with the other group members change. She approaches adult males (and occasionally females) to initiate mating, while other animals seek more contact with her. Mating takes generally a short time only.
If the egg is not fertilised, the mucous membrane of the uterus is flushed out of the body with menstrual bleeding, just as in humans. Bleeding lasts for 2-3 days and is considerably weaker than in humans.