210 G. H. PARKER 



observation the water in the pools contained decidedly less than 

 half as much oxygen as that in the flowing tide and that the 

 entrance of the tide into a pool quickly changed the water there 

 from a condition poor in oxygen to one relatively rich in this 

 gas. Another point of difference in the water of the pool and 

 that of the flowing tide was that the pool water had a tempera- 

 ture of about 27.5°C. and that in the inflowing tide 21.5°C. 



Experiments to ascertain the effect of the oxygen in the several 

 kinds of water on Metridium were conducted under the follow- 

 ing conditions. The pools, which were on Pine Island, in Woods 

 Hole, Massachusetts, were studied on clear days in August. 

 Work was begun as the tide was rising but before it had reached 

 the pools. In bright daylight almost all the specimens of 

 Metridium were retracted. Large battery jars were carefully 

 filled with water from the pools and into these jars stones were 

 put having attached to them several specimens of Metridium 

 in the retracted condition. The jars were allowed to stand in 

 the same exposure as the pool to determine whether the act of 

 transfering the sea-anemones would influence their conditions. 

 As a matter of fact the animals remained closed and gave no 

 evidence of being in any other state than that of the actinians 

 that remained in the pools. Careful transfer from pool to jar 

 is therefore not a source of disturbance to Metridium. 



If, now, pieces of stone on which there are closed actinians 

 are quickly transferred from the pools to the outside tidal water, 

 many of the sea-anemones on them will in a few minutes expand 

 their oral discs though their columns will remain contracted. 

 This response, though not invariable, was of such common occur- 

 rence that it was quite obviously typical of the transfer. It 

 must depend upon some difference between the two bodies of 

 water, for as has already been shown, the act of transfer in itself 

 is without significance. The difference between the two bodies 

 of water are differences of temperature, oxygen content, and 

 current action. 



To ascertain the effect of temperature, carefully collected pool- 

 water was cooled by being surrounded with ice from its initial 

 temperature of 27.5°C to that of the outside tidal water, 21.5°C. 



