1The adaptation of sleep and wakefulness to the 24-hour periodicity of night and day seems to reflect early ego development between the third and the fourteenth week of life, before the differentiation of the self from the environment is complete. Both the ego and the sleep rhythm evolve from an undifferentiated phase, when manifest behavior, homeostatic regulations, and congenital ego tendencies are inseparable, through an interrelationship between the infant's innate patterns of neurophysiological maturation and the response of the environment to his biological needs. The development of the sleep rhythm is mediated through the infant's relationship with his mother, communicated by her periodic absences or variations in responsiveness, which in

turn are influenced by her own adaptation to the 24-hour cycle of everyday life.