Just think: earthworms are hermaphrodites: They have 2 pairs of testes, surrounded by 2 pairs of testes sacs. There are 2 pairs of seminal vesicles which produce, store and release the sperm via the male pores, and ovaries and ovipores that release eggs via female pores. However, most also have one or more pairs of spermathecae (depending on the species) that are internal sacs which receive and store sperm from the other worm in copulation. Some species use external spermatophores for transfer instead.

The male reproductive organs consist of two pairs of testes, present ventro-laterally in the 10th and 11th segments. Each testis is made up of 4 to 8 processes containing spermatogonia. Each testis is enclosed in a pair of testes sacs which are filled with fluid. It is bilobed in the front and on the posterior side provided with a pair of ciliated spermaducal funnels, one on either side. Two pairs of seminal vesicles are present in the 11th and 12th segments which collect the sperm fluid. The testes sac of the tenth segment opens in the seminal vesicle of the 11th segment and testis sac of the 11th segment opens into the seminal vesicle of the 12th segment.

The sperm mother cells of the testes when shed offreach the seminal vesicle where they mature into sperms and then again passed into testes. Sperms from the testes are passed into the spermiducal funnels which lead into vas deferens. A pair of vasa deferentia on either side of nerve cord runs from the 12th segment to prostate region and opens out together with the prostate duct in the 18th segment as male genital aperture. The prostate is a large irregular gland present from the 16th to 20th or the 17th to 21st segments on either side, and it produces the prostate fluid. In the 17th and 19th segments each is found a pair of rounded, white fluffy masses, the accossory glands. These glands are present on ventro-lateral bodywall, one on either side of the nerve cord. They open to the exterior by a number of ducts in two pairs of genital pappillae, situated externally on either side of the mid-ventral line.

The female reproductive organs consist of a pair of ovaries, a pair of oviducts and four pairs of spermathecae.The ovaries are a pair of small, whitish, lobed structures, attached to the hinder face of the septum of the 12/13 segment, one on each side of the nerve cord.Each ovary has mature ova towards distal end and immature towards septal side.Each oviducal funnel leads into oviduct which opens outside in the 14th segment in the form of a common oviducal aperture.The four pairs of spermathecae are found on either side of the nerve cord in the 6th, 7th, 8th and 9th segments.Each spermathecae has two parts, a sac like structure, ampulla and a short diverticulum.The diverticulum stores the sperms while ampulla provides a nourishing fluid to them.These spermathecae open outside the bodyby four pairs of apertures one on either ventro-lateral sides of each segmental joint, i.e a pair in the 5-6, 6-7, 7-8, 8-9th segments.The mature ova shed from the ovaries, pass through the oviducal funnels into the oviduct and finally to the exterior through the female genital pore. Copulation and reproduction are separate processes in earthworms. The mating pair overlap front ends ventrally and each exchanges sperm with the other. The clitellum becomes very reddish to pinkish in color. The cocoon, or egg case, is secreted by the clitellum band which is near the front of the worm, but behind the spermathecae. Some time after copulation, long after the worms have separated, the clitellum secretes the cocoon which forms a ring around the worm. The worm then backs out of the ring, and as it does so, injects its own eggs and the other worm's sperm into it. As the worm slips out, the ends of the cocoon seal to form a vaguely lemon-shaped incubator (cocoon) in which the embryonic worms develop. They emerge as small, but fully formed earthworms, except for a lack of the sex structures, which develop later in about 60 to 90 days. They attain full size in about one year. Several common earthworm species are mostly parthenogenetic, that is, with asexual reproduction resulting in clones.

Isn't that fascinating?