28 Coelenterata. 



the nipple results from extreme contraction of the circular fibres immediately 

 proximal to the plane of cutting. Within a few days the elements of the tissues 

 near the cut are rearranged whereby results a permanent closure not dependent 

 upon muscular contraction. The closing of a distal cut end and the formation 

 of a nipple [s. supra] take place in a tentacle after it has been severed from 

 the column. When an excised tentacle is cut transversely into several pieces, 

 each piece shows a definite polarity, its two ends assuming different forms. 

 In any transverse zone of the tentacle two modes of response to transverse 

 cutting are potential^ present, one or the other being exhibited according as 

 the zone comes to lie at the proximal or distal end. No structural basis for 

 this polarity was found. 



Bohnf 1 ) states that although specimens of Actinia equina will live for several 

 months in filtered water they will do so only under certain conditions: a state 

 of physiological misery, sometimes leading to the death of the animal, is pro- 

 duced by insufficiency of either light or carbon dioxide. In the dark or in 

 obscure light the anemones cause a marked decrease in the amount of oxygen 

 in the water but in the light the amount of oxygen undergoes little or no 

 decrease and sometimes even increases. These facts support the view that two 

 phenomena are superposed, namely respiration and pigmentary assimilation 

 under the influence of light in the presence of carbon dioxide. 



Bohn( 2 ) has observed numerous cases of longitudinal fission of Anthea 

 cereus, into 2 or sometimes 3; this seems to be spontaneous fission and to form 

 a normal mode of reproduction. The fission took place as a result of the 

 active movements of the pedal disc; here it begins and, as the two portions 

 of the disc move in opposite directions, thence extends up the column. If the 

 impure water in which specimens have been kept for some days be replaced 

 by pure water a number of them divide the following morning. After fission 

 the two portions often exhibit different tropisms, for instance, one turns towards 

 the light, the other to the shade. In two cases auto to my of all the tentacles 

 of the outer cycle took place some hours after strong and prolonged insolation. 



Bohn( 4 ) gives a list of 36 factors which determine the reactions of Actinise 

 and emphasises the rhythmic character of their activity and the importance 

 of the light factor. Reversal of rhythm may be produced. Specimens of Aip- 

 tasia erythrochila kept in an aquarium in shallow water are fully expanded at 

 night but as the depth of water is increased the nocturnal expansion becomes 

 less and is replaced by expansion in the afternoon. The other reactions of these 

 specimens are also inverted: strong illumination in the morning or renewal of 

 the water causes retraction of the anemones with the former rhythm and ex- 

 pansion of those with the latter rhythm, thus in the same water and at the 

 same time the Actiniae in shallow water are retracted, those in deep water ex- 

 panded. Anemones react to contrasts either between their present and im- 

 mediately preceding conditions or between their present and habitual condition 

 at that hour. 



Bohn( 5 ) finds that Act. eq. and Sag. erythrochila live and remain expanded 

 in water very poor in oxygen, but tend to close under the influence of rapid 

 oxygenation. Closure of an anemone at night is not due to diminution of 

 oxygen but to diminution of light, the closure is more marked when the water 

 is artificially oxygenated. - - See also Bohn( 6 ) and van der Ghinst. 



Pieronf 1 ) concludes, from his experiments, that the variations in the amount 

 of the oxygen dissolved in the water in which specimens of Actinia equina 

 are living constitute one of the most important factors determining the reac- 

 tions of closure or expansion. Their anticipated reactions of closure as the 



