An octopus will only reproduce once during its lifetime. The male octopus will die within a month after releasing the sperm packets in to the female's mantle cavity. The female will spend nearly two months fertilizing, laying the eggs and caring for them before they hatch. With a few days of the eggs hatching the female also dies.
During that two month period she never leaves the eggs therefore she does not eat or sleep. She spends her days and nights gently blowing water towards the eggs to ensure they are receiving a sufficient amount of oxygen to survive.
Octopuses are highly intelligent, scientist have determined that they have the most complex brains of all invertebrates. They are capable of watching and learning and have been observed playing in captivity.
Octopuses also have a highly developed central nervous system which is comparable to humans and they feel pain the same a human does. They are also capable of feeling emotions on some level.
In the ocean mating occurs in deep water near large rock formations (providing the octopus with a sense of security.) An octopus reaches sexually maturity at about two years of age. The male will insert a special arm called a hectocotylus, his third arm on the right side. The arm is inserted in to the female's mantle cavity and the male releases sperm packets.
Once the eggs are fertilized the female will lay about 200,000 eggs of which only about a dozen will survive the first six weeks of life and actually take the shape of an octopus.
Once the eggs have been laid the female uses a string to attach them to her lair. She spends her time watching over the eggs and protecting them from predators and blowing water over them to provide them with oxygen. This last approximately 50 days during that time she will not eat or sleep.
Once the eggs have all hatched the female will die of starvation and exhaustion leaving the babies which are about the size of a grain of rice to survive on their own. They become part of the plankton that floats on the top of the water and if they are lucky enough to survive the first six weeks they will gradually start to sink towards the bottom of the ocean as the develop and take on the shape of an octopus.
The reproduction of the octopus is rather disheartening they basically exist to reproduce. The average lifespan of an octopus is only five years however, for the octopuses that reproduce it is almost half that at 2.5 years old.