THREE FIQURES
Changes in the rhythmic movements of the cirri of the rock barnacles, Balanus balaiioides and B. tintinabulum, have been used as criteria of the animals' response to several kinds of stimuli (Cole, '28,(28)(29) '30; Cole and Allison, '29,(29)(30)(30)(31). It has been noted that the cirri are extremely sensitive, but that the animal as a whole is very resistant to unfavorable environmental conditions, as is true of practically all animals with shells or valves capable of being tightly closed. A group of B. tintinabulum2 was removed from sea water at a temperature of from 11" to 16Β°C. and placed high above the water level on rocks exposed to the sun during August for twelve successive days. On some days the temperature of the rocks was well above 50Β°C.
Returned to sea water, the animals opened and established regular cirral movements within six hours. The lack of water, oxygen, and food, the inability to get rid of waste products, and the excessively high temperatures for such a long period, apparently caused no harm. B. balanoides" * A part of the expenses of this investigation was met by a grant from the American Association f o r the Advancement of Science, to which grateful acknowledgment is hereby made.