7. Anthozoa (incl. Hydrocorallia). A. Zoantharia. 23 



in the movement of the water in the rock-pool on the fall of the tide, as an 

 anticipatory reaction of defence against asphyxia. Specimens which live in the 

 higher littoral zone, where there is a notable nocturnal shortage of dissolved 

 oxygen, when placed in a limited supply of water, close much sooner than 

 individuals from the Laminarian region, which have never experienced im- 

 poverishment of the surrounding medium. The result is that the Laminarian 

 specimens, at the end of a given time, have consumed a greater quantity of 

 oxygen, and that they exhaust the medium more quickly. Specimens of A. eq. : 

 which had been kept in captivity for three or more mouths, were placed in a 

 rock-pool, alongside specimens found living there, but at the fall of the tide 

 seemed to be incapable of closing; they therefore lost a considerable part of 

 their water-content, and dried quickly during the interval between the tides. 

 Their sojourn in stagnant water had caused the loss of the anticipatory reaction. 

 But already at the end of about 14 or 15 tides the anticipatory closure was 

 clearly shown, although it was not as rapidly produced as in the controls. 



Schmid finds that after a specimen of Cereactis aurantiaca has been for a 

 time in complete darkness, withdrawal of the tentacles and elongation of the 

 body take place. If full daylight be then allowed to fall on the specimen the 

 body contracts and the tentacles spread themselves out rosette-wise, and the 

 rosette is turned towards the sun. In subdued light the animal moves into 

 the position of greatest light. Yellow and red rays exert a different influence 

 on the tentacles to green and blue. If Actinia sulcata be kept in the dark, 

 its tentacles droop and it assumes an attitude of sleep . On illumination an 

 immediate movement of the tentacles often takes place, but sometimes only 

 after several minutes. 



Cary( 2 ) has studied pedal laceration in Aiptasia and Cylista. The change 

 in the form of a laceration piece, leading up to the acquisition of the typical 

 actinian shape, takes place through the upgrowth of the tissue about the orifice 

 where it was torn off from the parent. The permanent mesenteries arise as 

 new growths in the undifferentiated tissues of the oral end of the laceration 

 piece. The first 12 mesenteries do not appear in the sequence followed by 

 those in embryos. As development proceeds, the old mesenteries those 

 brought over from the parent when the fragment was torn off become re- 

 stricted to a proportionately shorter and shorter part of the base of the young 

 actinian, and are finally resorbed. The mesenterial filaments are formed, 

 as in embryos, from a downgrowth of the ectodermal lining of the stomodasum. 

 Their trilobed condition arises by differentiation of this tissue. The tissues of 

 the most actively growing part of a laceration piece become very thin; the 

 ectoderm and endoderm lose all apparent cell-outlines; the mesogloea arises as 

 a direct continuation of that present in the older tissues. The newly formed 

 tissues contain a very small number of gland-cells and nematocysts. These 

 two types of cells are developed to the usual number after the tissue-relations 

 have become stable. 



Roaf records a specimen of Actinoloba dianthus which showed partial 

 fission. When one of the two mouths present was given food stained with 

 neutral red, the neighbouring tentacles became pink and remained coloured for 

 4 weeks, while those around the other mouth remained white. When one oral 

 disc was stimulated its tentacles contracted but those of the other disc only 

 did so after a slight interval, and probably as a result of the pull caused by 

 the contracted state of the neighbouring body. Therefore there was no com- 

 munication between the two coelentera, and no direct nervous connection be- 

 tween the two division-products. 



