Early steps in the regeneration of the musculature in Macrostomum sp (Macrostomorpha)

Macrostomum sp., a microturbellarian from the Northern Adriatic, is able to regenerate only its posterior end after artificial surgery. Restoration of muscle tissue is one of the early events in regeneration. Morphallactic and epimorphotic processes occur simultaneously and consecutively. Shortly after surgery, rearrangement of muscles near the wound was observed. Six to eight hours later a faint transient network of muscle fibres was visible in the parenchyma at the site of the future blastema. One day after surgery an outgrowth of existing longitudinal fibres beneath the epidermis surrounded the developing blastema. At the caudal end of these fibres excessive forking was observed. New myocytes for circular musculature perpendicular to the growing longitudinal muscles were visible around the blastema. One week after surgery the adhesive plate and all muscles of the male copulatory organ were completely regenerated, after another week the regenerate had reached the length recorded prior to surgery.