Abstract
The acetylcholine esterase cone, in the several gross divisions of the C. N. S., in skeletal muscle and in liver was detd. on the human for the fetal period by a pharmacological method. Correlation of these studies with the developing motility and behavior reveals a significant relationship. The period of most rapid cone, of the enzyme in the several gross divisions of the C. N. S. seems to parallel their functional development. The liver has its highest cone, of acetylcholine esterase in the early fetal stage.