C. C. SPEIDEL (Amer. Scientist, 36, 237; 1948) describes with some very fine illustrations the results he has obtained by fast cinematography of cells inside the living animal. He used regenerating tail tissue of the tadpole for his observations, and shows that cellular organisation may be studied here with results which tissue cultures cannot provide. Regeneration of nerve fibres, showing the manner in which their direction and anastomosing take place, mitosis in a nerve cell and the relative movements of the two daughter nuclei, the movement of lymphocytes and diapedesis of leucocytes are among the many beautiful results of this method of observation. The salvaging of extravasated blood cell by cell by the sprouting of a lymph vessel is startling, while the movement of muscle fibres in contraction and relaxation may be followed step by step. It would seem that this method of analysis would be of great value in further studies of development, especially in the little-known differentiation of plant tissues.