COMPLEX RESPONSES 159 



lected pool-water was cooled by being surrounded with 

 ice from its initial temperature of 27.5 degrees centigrade 

 to that of the outside tidal water, 21.5 degrees centigrade. 

 Into this cool pool-water pieces of rock on which were 

 closed actiiiians were introduced from the pools, and the 

 animals watched. They remained contracted for over 

 an hour and it was concluded that the expansion of the 

 sea-anemones when transferred from the pools to the out- 

 side tidal water was not due to the difference in 

 temperature. 



Pool-water was now collected and thoroughly aerated 

 by being poured back and forth from one jar to another 

 many times, but when placed in this the sea-anemones 

 also failed to expand. Some of this water on being ex- 

 amined proved to contain 7.33 milligrams of oxygen 

 per 1000 cubic centimeters. It is, therefore, clear that 

 Metridium does not expand in the running tide because 

 of the increase of oxygen. 



Finally two jars were so arranged that one conducted 

 water into the other through a large siphon in such a 

 way as to expose the flowing water to air as little as pos- 

 sible. The upper jar being kept full of pool- water, sup- 

 plied the lower jar from which the water was in continu- 

 ous overflow. In this way pool-water was given a current 

 without changing in any marked degree its temperature or 

 its oxygen content. When closed specimens of Metridium 

 on bits of rock were introduced into the jar through which 

 the water was flowing, they very commonly expanded 

 their oral discs though their columns remained short. It, 

 therefore, seems clear that the motion of the tide water, 

 rather than its lower temperature or greater oxygen con- 

 tent, was the element responsible for the expansion of 

 Metridium under the circumstances noted. As a check 



