ACTINIAN BEHAVIOR 209 



few minutes, whereas those in the other dish will remain almost 

 to an individual retracted. It was quite clear to me from obser- 

 vations of this kind that the dissolved products from the food 

 of the sea-anemone would induce the expansion of its oral disc 

 though this agent had very little effect on the shortened condi- 

 tion of the column in these animals. 



The part played by oxygen in the expansion and retraction 

 of sea-anemones has been a matter of recent dispute. Accord- 

 ing to Pi^ron ('06 b) Actinia equina opens in seawater with a 

 large oxygen content and closes when there is a deficiency of 

 this gas. Pieron ('08 a, '08 b, '09) as a result of further investi- 

 gations was led to believe that not only did oxygen have this 

 effect but that it was one of the most important factors in deter- 

 mining expansion and retraction. Bohn ('08 a, '08 c, '10 a) on 

 the other hand maintains that Actinia equina will remain ex- 

 panded in seawater containing very little oxygen 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 differences of opinion it is difficult to arrive 

 at any conclusion without further observation. 



All the experiments that I made to ascertain the importance 

 of oxygen in retraction and expansion were carried out on 

 Metridium marginatum at Woods Hole, Massachusetts. Speci- 

 mens of this species were studied in rock pools which were 

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

 content of the seawater from the several situations involved was 

 determined by the Winckler method. I am under obligations 

 to Dr. H. Wasteneys for having made these determinations for 

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

 tain 7.06 mgm. of oxygen per 1000 cc. The water in a small 

 undisturbed pool just previous to the entrance of the tide con- 

 tained 3.15 mgm. of oxygen per 1000 cc, while that in the undis- 

 turbed end of a pool into which the tide was beginning to flow, 

 contained 2.76 mgm. At the end of the pool into which the 

 tide had entered, the oxygen was found to be 7.02 mgm. per 

 1000 cc. From these figures it is evident that at the time of 



THE JOURXAL OF EXPERIMENTAL ZOOLOGY, VOL. 22, NO. 2 



