Analogous phenomena have been observed by Drzewina (1907), in the charming little hermit crab of our coasts, the misanthropic Pagurus (Clibanarius misanthropus), which is found in abundance upon the littoral of the Gulf of Gascony and in the Mediterranean.
In the harbor of Arcachon, near the wharf where Drzewina made his first experiments, the tide is high from noon to six o'clock during the eight hours of the tide, low for the same time during the eight following hours, which are those of low water, and it is stated that during the first period the Pagurus runs freely on the bottom, while it hides under the rocks during the second period. This phenomenon is undoubtedly due to the lighting of the sea-floor, which is only moderate during the first period on account of the depth of the water, and intense during the second, when the depth of the water, which softens the rays, i's greatly reduced. At any rate, it seems to be an acquired rhythm. If, as a matter of fact, one places these creatures in an aquarium partly covered with a black screen, they are seen in the light part during the period and at the time when the sea is at high tide, but under the black screen during the hours and at the period which correspond to the low tide. However, this acquired rhythm has not yet become specific and is closely related to the conditions of the environment, and in the Mediterranean, where the tides are not great, the observer has noticed that the Pagurus does not show the least periodicity.