During copulation the head ends of the two worms are directed in the opposite directions and the clitellum of one worm is opposite to the spermathecal segments of the other. The spermatozoa of one worm pass into the spermathecae of the other worms. The worms separate after the mutual exchange of spermatozoa.
Later the glandular cells of the clitellum secrete a thick fluid which hardens into a girdle surrounding the clitellum.
The girdle is moved forward by the wriggling movements of the body. As the girdle is moved forwards it receives the ova and spermatozoa. The girdle con-taining the germ cells (ova and sperms) and the nutrient albuminous fluid is slipped off at the anterior end and it becomes a closed sac called the cocoon. Fertilization and the development of the eggs into worms takes place within the cocoon. Young worms come out of the cocoon after complete development.