152 THE ELEMENTARY NERVOUS SYSTEM 



The influence of light on actinians is by no means uni- 

 form but differs with different species. According to 

 Nagel (1894, 1896), Adamsia, Anemonia, 1 and Actinia 

 are not responsive to light. Fleure and Walton (1907) 

 have noted this lack of response in Anthea as well as in 

 Adamsia. Pieron (1906 c, 1908 <?) has confirmed Nagel 's 

 statment for Actinia. Although this lack of response may 

 be true of the forms just mentioned, it is certainly not 

 true of Metridium marginatum or Sagartia IUCICB, for, 

 though Hargitt (1907) was unable to get responses to 

 light from these species, both will close quickly on bright 

 illumination. This is in agreement with Bonn's observa- 

 tions (1906 a) as well as with Gosse's account (1860) of 

 the closely allied species, Metridium dianthus. Concern- 

 ing 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 beauties ; but an 

 hour of darkness will often suffice to overcome the reluc- 

 tance 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 night- 

 fall." Retraction under bright illumination has also 

 been recorded for a number of actinians among which 

 are the following: Edivardsia 2 (de Quatrefages, 1842; 

 Fischer, 1888), Cerianthus 2 (Haime, 1854; Nagel, 1894; 

 Hess, 1913), Phillia (Gosse, 1860), various species of 



1 Bohn ( 1907 c) states that Anemonia is not entirely 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. 



'These instances, Edivardsia and Cerianthns, are often attributed to 

 Bronn (1860) who apparently simply repeated the statements made by 

 de Quatrefages and by Haime without giving references. 



