title: Stages of sleep evolution (facts and hypotheses).
abstract: The paper contains new data concerning the peculiarities of sleep in poikilotherms (fish, amphibians, reptiles). A conclusion is drawn that sleep and the activation spontaneously arising against its background are the universal phenomena in vertebrates. A supposition is argued about the existence of evolutionary succession between the forms of sleep inherent in lower vertebrates and the quiet and active phases of homoiotherms' sleep.
mesh_terms: D000663:Amphibians / Q000502:physiology*; D000818:Animals; D005075:Biological Evolution; D004569:Electroencephalography; D005399:Fishes / Q000502:physiology*; D009424:Nervous System Physiological Phenomena; D010507:Periodicity; D012104:Reptiles / Q000502:physiology*; D012894:Sleep Stages