Octopus mating is accomplished by the male using one of his arms to insert a sperm sac into the female where the sac survives until the eggs are released from the female and fertilized with the sperm outside of the female’s body. The eggs are not fertilized inside the female. The eggs are methodically fertilized by the female octopus by spreading the sperm over the eggs after they are laid.
Octopus mating is a one-time occurrence for each octopus since the male dies within months of finding a mate and the female dies shortly after the eggs are laid. The female can lay up to 200,000 eggs at once but only about 1/3 survive to adulthood.