158 THE ELEMENTARY NERVOUS SYSTEM 



27.5 degrees centigrade and that in the inflowing tide 

 21.5 degrees centigrade. 



Experiments to ascertain the effect of the oxygen in 

 the several kinds of water on Metridium were conducted 

 under the following conditions. The pools, which were on 

 Pine Island, in Woods Hole, Massachusetts, were studied 

 on clear days hi August. Work was begun as the tide was 

 rising, but before it had reached the pools. In bright day- 

 light almost all the specimens of Metridium were re- 

 tracted. 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 transferring 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 actin- 

 ians are quickly transferred from the pools to the out- 

 side 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 occurrence 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 col- 



