7. Anthozoa (incl. Hydrocorallia). A. Zoantharia. 25 



Bohn( 1 ) has studied the curving of the column of Actinoloba dianthus which 

 is much elongated in water charged with carbon dioxide and other excretory 

 products, and becomes very sensitive to variations of light, tending to turn 

 itself towards the lightest surface but generally only arriving at a stable position 

 after a series of rotations or oscillations. Bohn( 2 ) finds that Anthea cereus 

 is very sensitive to variations of light. In a feeble illumination the tentacles 

 are extended perpendicular to the light rays, but as the light becomes more 

 intense the tentacles, first the internal then the external, converge forming a 

 bundle parallel to the direction of the light rays. In this way the anemone 

 is protected against a light which is too strong and assimilation does not sensibly 

 vary. When the water becomes impure the fasciculation of the tentacles takes 

 place more easily, i. e., is caused by a more feeble illumination than before. 

 When specimens have been for a long time (18 days) in impure water and 

 are then placed in pure water, the tentacles remain in a bundle even- in feeble 

 illumination. The fasciculation of the tentacles also takes place more readily 

 after a moderate period (6-9 hours) in the dark, but after 24 hours in the 

 dark the tentacles remain flaccid and drooping. The animal has the power 

 of orientation of its tentacles in order to regulate the assimilation of carbon 

 dioxide by an associated alga. 



Bohn( 3 ) shows that specimens of Actinia equina removed from a vertical 

 face of rock exposed at every tide, and placed in an aquarium under invariable 

 conditions become closed at the time of low-water and open again at the 

 period of high-water. Such periodicity lasts for at least 8 days, but gradually 

 disappears and, in specimens kept in an aquarium, is replaced by a new periodi- 

 city corresponding to day and night. - - According to Bohn & Pieron specimens 

 of A. e. living between tide-marks and subjected to rise and fall of tide undergo 

 successive opening and closing; there is a biological association between these 

 phenomena. After the rhythm has become impressed the actinian no longer 

 awaits the effective cause which brings about the reaction but reacts before- 

 hand (reflex anticipation). Pieron states that specimens living on the rocks 

 between tide-marks close when the sea retires whether they are left dry or 

 in pools, but their tentacles expand again on the return of the sea. The 

 actinians open on agitation of the water and oxygenation (as by the incoming 

 tide) and on excitation by means of food; they close if left dry or in defect 

 of oxygen (as at low-tide) or if cut or subjected to toxic (chemical or osmotic) 

 modifications of the medium in which they are living. 



Child(') finds that supplementary partial discs, with a number of ten- 

 tacles corresponding to that portion of the whole circumference which they 

 represent, can be produced from lateral transverse cuts in the body-wall of 

 Cerianthus. If the lateral cut is in the cesophageal region and is deep enough 

 to involve the oesophagus the supplementary disc possesses a mouth, because 

 the cut surfaces of the body-wall unite with those of the oesophagus, thus 

 forming a second opening into the oesophagus. If the cut is below the oesophageal 

 region the supplementary disc possesses no mouth. In the extreme aboral 

 region of the body the formation of supplementary discs does not occur. When 

 the lateral cut is made in the cesophageal region, permanent collapse and 

 atrophy of the tentacles and region directly above the cut occur, or if these 

 structures have been removed their regeneration is retarded and atrophy occurs 

 after a time. This collapse and atrophy are due to decrease in the internal 

 water-pressure, as the enteric cavity of the region above the cut is completely 

 shut off from the general enteric cavity and from the exterior. In two cases 

 the formation of tentacles was observed in the aboral end of a piece of certain 



