The mitotic pattern of the nerve cord during the growth of an anouranaquatic Amphibian is more similar to that of an aquatic Urodelan than to that of another Anouran, but terrestrial; this indicates that the mitotic ratio in the Amphibians is affected by ecologic factors, but non by philetic ones. The persistence of mitotic activity and some regenerative events in the spinal cord of adult Anourans postulate that the nervous system in Amphibians is a tissue formed by stable cellular elements.