The process of copulation in earthworm
The spermatozoa of one worm are transferred to another during a process called copulation. It generally takes place at night, from July t.o October. This process lasts for about one hour. During copulation, two worms apply to each – other by their ventral surface. They point their head ends in opposite directions. In this position, the male genital aperture of each lies against the spermathecal pores ofthe other. The two copulants are probably held together in two ways by mutual penrrtration of setae in each other’s body and by production of sticky substance from their clitellum and genital papillae. The areas surrounding the male genital pores of each worms are raised into papillae, which are inserted successively from behind forwards, into the spermathecal pores of the other worm and discharge the spermatozoa. These sperrnatozoa are stored in the spermathecae of the partner. Earthworms are bisexual, still self-fertilization does not occur. They cannot fertilize their own eggs because the testes mature earlier than ovaries (protrandous). This makes self-fertilization impossible. Thus, cross fertilization takes place accompanied by copulation. After the interchange of spefiirs, the two worms separate and later lay their eggs in cocoons. Fertilization is external, taking place inside protective cocoons. The cocoon is secreted as gelatinous, viscid and sticky collar or girdle around the clitellum. It hardens gradually on exposure to the air into a tough elastic cocoon. As the worm wriggles behind, the cocoon is slipped forwards towards the head- On its way it receives several ova from the female genital pore and sperrnatozoa from spermathecae pores. Finally the cocoon is thrown off the head, and its both the elastic ends close up. Fertilization or fusion of gametes occurs inside the cocoon when it get deposited in moist earth.