When octopuses reproduce, they use a specialized arm called a hectocotylus to insert spermatophores (packets of sperm) into the female's mantle cavity. The hectocotylus is usually the third right arm. In some species, the female octopus can keep the sperm alive inside her for weeks until her eggs are mature. After they have been fertilized, the female lays roughly 200,000 eggs (this figure dramatically varies between species). The female hangs these eggs in strings from the ceiling of her lair. After the eggs hatch, the young larval octopuses must spend a period of time drifting in clouds of plankton, where they feed on copepods, larval crabs and larval seastars until they are ready to sink down to the bottom of the ocean, where the cycle repeats itself. In some deeper dwelling species, the young don't go through this period. This is a dangerous time for the larval octopuses. As they become part of the plankton cloud they are preyed upon by the many other plankton eaters.
Octopuses are also quite strong for their size. Octopuses kept as pets have been known to open the covers of their aquariums and survive for a time in the air in order to get to a nearby feeder tank and gorge themsleves on the fish there.
A common belief is that when stressed, an octopus may begin to eat itself. However, limited research conducted in this area has revealed that the cause of this abnormal behaviour may be a virus that attacks the octopus's nervous system. Thus this behavior may be more correctly labeled as a mental disease.
Fowler's Modern English Usage states that "the only acceptable plural in English is octopuses", and that octopi is misconceived and octopodes pedantic. Octopi derives from the mistaken notion that octopus is a second declension Latin noun, which it is not. Rather, it is (Latinized) Greek, from oktopous , gender masculine, whose plural is oktopodes. If the word were Latin, it would be octopes ('eight-foot') and the plural octopedes, analogous to centipedes and millipedes, as the plural form of pes ('foot') is pedes.
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