Biological rhythmicity has been a subject of scientific research for a relatively short time. In the special case of daily, or circadian rhythms, it is only during the past twenty years that rapidly increasing efforts have been undertaken in evaluat ing properties and mechanisms. As a consequence of these efforts, the study of biological and, in particular, circadian rhythmicity is no longer a somewhat dubious occupation but rather a serious branch of science which combines the interdisciplinary efforts of numerous researchers around the world. The general result of these efforts is that many...