Since the beginning of the 19th century, the comparative and ontogenetic branches of developmental physiology were cultivated in our country. Evidence was given that development of the gastrointestinal tract in tadpoles is dependent on the quality of proteins in their food. A complete metamorphosis of Amblystoma mexicanum, was entirely accomplished by feeding with powderized thyroid gland. The definition and chronological delimitation of both the suckling and weaning period in experimental animals opened the investigation of the effect of disturbance of the natural environment caused by premature weaning on the ensuing development of an individual. A new term was coined "late effects of early adaptations". Analysis was provided by impressive research of the development of energetic metabolism and development of gastrointestinal tract functions, water and electrolyte exchange and endocrine functions including the role of the pineal gland in control of circadian rhythms (12 references).