ABSTRACT
Sleep is necessarily a spare-time activity. It has to be so because it can only be indulged in when all of the essential activities of life have been completed. The discovery that fish sleep comes as something of a surprise to most people. Even sleep theorists have largely ignored the fact that the sleep which they are studying in humans is really quite common among remote animals. It has been suggested that sleep helps to reprogramme our sophisticated computer-like brains. Larger reptiles such as the crocodile spend enormously long periods in a state of complete immobility which must not be confused with sleep. Frogs, toads, newts and salamanders have also been studied and shown to have long periods of sleep-like immobility. An automatic sleep/wake scheduling mechanism is clearly valuable for those animals who need only a few hours of activity each day to carry out all essential activities.
