Hemimetabolous metamorphosis, also known as incomplete metamorphosis, involves three stages: egg, nymph, and adult. The nymph stage resembles a smaller version of the adult and gradually matures without undergoing a pupal stage. On the other hand, holometabolous metamorphosis, or complete metamorphosis, involves four distinct stages: egg, larva, pupa, and adult. The larval stage is morphologically different from the adult, and the transformation to the adult form occurs during the pupal stage.