Leeches are hermaphrodites, meaning they are organisms that have both female and male reproductive organs (ovaries and testes respectively). They reproduce by reciprocal fertilization and sperm transfer occurs during copulation.The leech exercising the role of the male will grow a sperm sack near the end of their tail, and the leech playing the female will bite it off, thus reproducing. Similarly to the earth worms, leeches also use a clitellum to hold their eggs and secrete the cocoon.
During reproduction leeches utilize hyperdermic injection of their sperm. They use a spermatophore which is a structure containing the sperm. Once next to another leech, the two will line up with their anterior side opposite the others posterior. The leech then shoots the spermatophore into the clitellur region of the opposing leech where its sperm will make its way to the female reproductive parts.