ACTINIAN BEHAVIOR 205 



will extend itself to as much as six times the diameter of its 

 column, and hold its oral disc fully opened. In no instance 

 have I ever found in nature a degree of expansion greater than 

 that seen in the laboratory under the circumstances just stated. 

 This maximum degree of expansion under natural circumstances 

 has often been observed in sea-anemones in pools during the night 

 or even during the day in dark situations such as under bridges 

 and so forth. The elements that contribute to this extreme 

 expansion are certainly diverse. Of these I have tested light, 

 temperature, food, oxygen supply, and water currents. 



The influence of light on actinians is by no means uniform 

 but differs with different species. According to Nagel ('94, p. 

 545; '96, p. 33) Adamsia, Anemonia- and Actinia are not respon- 

 sive to light. Fleure and Walton ('07, p. 217) have noted this 

 lack of response in Anthea as well as in Adamsia. Pieroh ('06 c, 

 p. 44; '08 c, p. 1021) has confirmed Nagel's statement for Actinia. 

 Although this lack of response may be true of the forms just 

 mentioned, I have not been able to demonstrate it in Metridium 

 marginatum nor in Sagartia luciae, both of which according to 

 Hargitt ('07, p. 280) are said to be quite indifferent to light. 

 My observations on these species leave no doubt in my own 

 mind that both close quickly on bright illumination. This is 

 in agreement w4th Bohn's observations ('06 a, p. 421) as well 

 as with Gosse's account ('60, p. 15) of the closely alhed species, 

 Metridium dianthus. Concerning this form Gosse remarks that 

 ''it is under the veil of night that the anemones in general 

 expand most readily and fully. While the glare of day is upon 

 them, they are often chary of displaying their blossomed beau- 

 ties; but an hour of darkness will often suffice to overcome the 

 reluctance of the coyest. The species before us," M. dianthus, 

 ''is not particularly shy; it may often be seen opened to the full 

 in broad daylight; but if you would make sure of seeing it in 

 all the gorgeousness of its magnificent bloom, visit your tank 

 with a candle an hour or two after nightfall." Retraction under 



- Bohn ('07 c) states that Anemonia is not entirel}^ without response to light. 

 In weak light it is said to place its tentacles at right angles to the rays and in 

 strong light parallel to them. 



