This is the first detailed behavioral study of Paramecium thermotaxis (note that as I am not a German speaker, this review is based on an automatic translation). When placed in a temperature gradient, paramecia tend to gather in regions at 24-28 °C. Thus, they display both positive and negative thermotaxis, depending on the temperature. This preferred temperature zone is in fact not fixed. If paramecia are kept for several hours at a higher temperature, the favorite temperature zone shifts accordingly. Thus, paramecia adapt to temperature, and thermotaxis seems to implement some form of homeostasis: paramecia move towards temperatures to which they are physiologically accustomed. The mechanism of thermotaxis is not described, but Mendelssohn seems to favor a sensitivity to the spatial temperature gradient over the cell’s length (for which he gives an estimate of about 0.01 °C). Later studies showed that this is incorrect; instead, paramecia give the avoiding reaction and change direction in reaction to temporal changes in temperature (Nakaoka & Oosawa, 1977).