[Comparative study of the cells of the freshwater planarian Polycelis tenuis (Iijima) using dissociated fragments cultivated in vitro: ultrastructural aspects and incorporation of (3H) leucine and (3H) uridine].

Study of planaria cells, which are the result of dissociated fragments cultivated in vitro, allows the evolution of two cell groups to be followed: (1) Differentiated cells, which do not divide, and do not dedifferentiate either, incorporate leucine and uridine at a rate which remains stable for the whole duration of the culture. (2) Undifferentiated cells have a mitotic and incorporation rate of leucine and uridine which varies during the period of culture. After 10 days of culture they demonstrate the characteristics of cells undergoing differentiation. These results are in agreement with those of other authors who attribute an essential role to undifferentiated cells during regeneration of the adult planaria.