Final answer:
Earthworms reproduce by mutually exchanging sperm since they are hermaphroditic; they do not self-fertilize. After the exchange, internal fertilization occurs, and a mucous cocoon is produced which holds the developing embryos.
Step-by-step explanation:
During typical earthworm reproduction, hermaphroditic individuals exchange sperm.
Earthworms are hermaphrodites, meaning each individual has both male and female reproductive organs. Unlike some hermaphroditic species that can self-fertilize, earthworms engage in a mutual exchange of sperm with another earthworm.
This process involves two earthworms aligning their bodies ventrally and exchanging sperm via their reproductive openings. The sperm are then stored and later used to fertilize the eggs internally. Once fertilized, the embryos are encased in a protective mucous cocoon, from which fully formed juvenile earthworms eventually emerge, skipping any larval stage and growing directly to adult size.