COMPLEX RESPONSES 157 



on the other hand, maintains that Actinia equina will 

 remain expanded in seawater containing very little oxy- 

 gen and will close when that water is richly oxygenated. 

 In the opinion of this investigator the states of expansion 

 and retraction are due chiefly to light and darkness and 

 not to the supply of oxygen. In the face of such differ- 

 ences of opinion it is difficult to arrive at any conclusion 

 without further observation. 



Specimens of Metridium marginatum in the rock pools 

 at Woods Hole, Massachusetts, were therefore studied. 

 The pools in which these sea-anemones were located were 

 flooded at high tide and left isolated at low tide. The 

 oxygen content of the seawater from the several situa- 

 tions involved was determined by the Winckler method. 3 

 The outside water on the incoming tide was found to con- 

 tain 7.06 milligrams of oxygen per 1000 cubic centi- 

 meters. The water in a small undisturbed pool just 

 previous to the entrance of the tide contained 3.15 milli- 

 grams of oxygen per 1000 cubic centimeters, while that 

 in the undisturbed end of a pool into which the tide was 

 beginning to flow, contained 2.76 milligrams. At the 

 end of the pool into which the tide had entered, the oxygen 

 was found to be 7.02 milligrams per 1000 cubic centi- 

 meters. From these figures it is evident that at the time 

 of 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 dif- 

 ference in the water of the pool and that of the flowing 

 tide was that the pool water had a temperature of about 



*The determinations were made by Dr. H. Wasteneys. 



