Earthworms
Earthworms mate at night on the surface. Earthworms have both male and female sex organs. They have one or two pairs of testes. There are two or four pairs of seminal vesicles, which produce, store, and release the sperm. Ovaries and oviducts release eggs. Copulation (animal sexual behavior) and reproduction are two different processes in earthworms. The mating pair overlaps front ends and each exchanges sperm with the other. Some time after copulation, long after the worms have separated, a cocoon is formed around the worm and it slips out of the cocoon. As it does so, it injects its own eggs and the other worm's sperm into it. The cocoon is sealed and the worms develop in it. They emerge as small, but fully formed earthworms, but lack their sex structures, which develop in about 60 to 90 days. They reach full size in about one year.