The Moro reflex, reported by Moro1 in 1918, is a complex response in which the arms are extended at the sides to approximate an arch and then slowly brought together one over the other in front of the body. The legs execute a similar movement. It is found only in very young infants and has usually disappeared by the end of the fourth month. The stimulus most commonly used to elicit it is a sudden blow on the bed or table on which the infant is supported. Other stimuli, such as tapping the abdomen, extending the legs at the hips, blowing on the face,2 cold or warm applications to the trunk and sudden movement through space,3 will also elicit the response. Moro, stressing the second, "clasping" phase of the reflex rather than the primary extension, saw in this behavior a primitive, atavistic response the purpose of which