Plant and animal rhythms have caught the attention of astute observers throughout history, but it was not until the eighteenth century that research in the area really began. Of the many rhythms we casually observe in the creatures around us, the most familiar is the daily rhythm of activity and rest. Ordinarily, the cues of daylight and darkness help to keep plants and animals synchronized with the environment. But neither honeybees, plants, nor man depend entirely upon such cues—all will show their "time sense" even when isolated from the outside world in a deep mine, cavern, or similar situation. In such cases the organism is said to "free run," that, is, a more nearly inherent rhythm appears. This rhythm is approximately 24 hours and is usually called circadian, meaning around a day. This period is found to be a constant feature of plants and animals, leading some researchers to conclude that it is a fundamental attribute of protoplasm. The literature on biological clocks or circadian rhythms dates back to the early 1950's. Many books such as The Physiological Clock by Professor Erwin Sunning, The Living Clocks by Ritchie Ward, Biological Rhythms by Reinberg and Ghata, and Of Time, Tides, and Inner Clocks by Henry Still, are available on the subject as It relates to various organisms, including man. Fiddler crabs, lugworms, and Drosophila have been studied extensively with regard to circadian rhythms. Earthworms are reported by J. L. Cloudsley- Thompson (4) as being polyphasic showing about 4 rest and activity periods In the 24 hour cycle and by J. Arbit (1) In "Diurnal Cycles and Learning In Earthworms" as learning better between 8 and 12 P.M. However, while much has been written about circadian rhythms In these and other organisms and about regeneration in Dugesia tigrina, the common fresh water planarian, there is little published information with regard to circadian rhythms In planaria. The purpose of this investigation was: 1. to ascertain the peak/peaks—low/lows In the circadian rhythm of Dugesia tigrina and 2. to determine if such extremes in rhythm have a corresponding effect on the regeneration of worms transected during those periods.
Brandt, Mary Michael, "Circadian Rhythm in Dugesia Tigrina and Its Correlation With Regeneration" (1974). Theses & Dissertations. 67.