Hypophysectomy of the adult frog inhibits cell division in the lens epithelium. Hypophysectomy, replacement therapy with hypophysial hormones and needle injury of the lens are used to study cells inG₀ G1 and M. Cells in G₀ are characterized by a lack of rough endoplasmic reticulum, mitochondria and ribosomes. Cells in G1 are characterized by an increase in these organelles. Cells in M are characterized by cytoplasm containing no observable rough endoplasmic reticulum and practically no mitochondria; but many vesicles are present. Injuries of the lens from hypophysectomized frogs are compared to similar injuries in intact frogs. Possible differences are discussed.