ACTINIAN BEHAVIOR 211 



Into this cool pool-water pieces of rock from the pools on which 

 were closed actinians were introduced, and the animals watched. 

 They remained contracted for over an hour and it was con- 

 cluded that the expansion of the sea-anemones when transferred 

 from the pools to the outside 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 examined proved to contain 7.33 

 mgm. of oxygen per 1000 cc. 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 possible. The upper jar 

 being kept full of pool-water, supplied the lower jar from which 

 the water was in continuous 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. I there- 

 fore concluded that the motion of the tide water, rather than its 

 lower temperature or greater oxygen content, was the element 

 responsible for the expansion of Metridium under the circum- 

 stances noted. As a check on this conclusion several vessels 

 were filled with tidal water and after it had come to rest stones 

 carrying Metridium were introduced into it. Although this quiet 

 tidal water retained its characteristically lower temperature and 

 its higher oxygen content, the sea-anemones remained closed in 

 it, thus confirming the conclusion already expressed that motion 

 is the element in tidal water that induces expansion. 



The effect of water currents and other forms of agitation were 

 not only observed under natural conditions but were tested 

 likewise in the laboratory. If a Metridium is put in a darkened 

 vessel through which seawater is running, it quickly assumes 



