22 Coelenterata. 



was unaccompanied by the excessive discharge of nettle capsules and of slime 

 and in other respects resembled the reversal produced in normal feeding. The 

 latter is due chiefly to the chemical action of organic molecules, and not to ion 

 action, though potassium ions, if sufficiently concentrated, will cause reversal. 



Allabach finds that after a specimen of Metridium marginatnm has swallowed 

 10 or 12 pieces of meat the outer tentacles no longer react, but meat placed 

 on the inner tentacles is slowly transferred to the mouth and swallowed; finally 

 all the tentacles cease to react, but meat placed directly on the mouth is in- 

 gested, apparently by the action of the cilia. The reversal of the cilia seems 

 to be more nearly independent of the physiological states of the animal than 

 are the contractions of the muscles. The mouth never reaches a condition 

 where it rejects pieces of mussel placed directly upon it. The loss of reaction 

 of the tentacles is not due to fatigue for - - (1) if a specimen is fed from one 

 side of the disc till satiated, meat is refused by tentacles of the other side 

 although these latter cannot have become fatigued, (2) seven hours after feed- 

 ing to repletion the tentacles, though they have had this period for recuperation, 

 still refuse to take food. Pieces of filter-paper are readily taken by hungry 

 specimens , but after having been well fed, paper is refused first by the outer, 

 later by the inner, tentacles, and finally by the mouth. The rejection of paper 

 is not due to the animal's experience of any effectsproduced by paper in its 

 coslenteron, because if the paper is withdrawn from the stomoda:um so that it 

 never reaches the coelenteron, the animal conies to reject paper as quickly as 

 before. After placing meat or meat juice a dozen times on the same region 

 of the disc the animal rejects filter-paper in this region, the same result being 

 reached if the pieces of meat are removed after passing into the stomodseum. 

 Thus repetition of strong stimuli, of weak stimuli, and of these alternately, 

 produces the same effect, namely the animal ceases to react to weak stimuli. 

 This is evidently due to fatigue, but this lasts only for 2 to 5 minutes, after 

 which the fatigued region is frequently as ready to take food as before, if 

 the animal is still hungry. 



Duerden( 2 ) describes the feeding and other reactions of Cribrina, Fungia 

 and Favia. Small non-nutritive particles falling on the disc and tentacles 

 become embedded in a superficial layer of mucus which is Always present, 

 they may remain there for some time dependent upon the activity of the polyp, 

 but finally the mucus is broken up and with the imbedded particles is carried 

 away by the exhalent currents from the stornodseum. Nutritive substances cause 

 an opening of the mouth, the establishment of an inhalent stomodseal current 

 and a more rapid secretion of mucus, surrounded by which the substances 

 are drawn into the coelenteron. When an inhalent current has been established 

 objects are indrawn independently of their nutritive value. In Actinians the 

 transference of food to the mouth is largely assisted by the movements of the 

 tentacles, disc and upper part of column; but in corals the stomodaeal currents, 

 assisted by the secretion of mucus, are the principal agents. A complex system 

 of mucous streams is well shown- in compound corals. The movements of 

 heavier particles over the disc is largely due to thigmotactic or recovery re- 

 actions on the part of the polyp, important in view of the conditions under 

 which many Actinians and corals live. 



Thomson & Simpson describe Cirripathes (?) In., Antipathes 3 (2 n.), Sticho- 

 pathes 4 (3 n.) and 1 n. var., Antipathella 4 n. (the polyps of most of these being 

 also described) and draw attention to the great variations in the form and dis- 

 tribution of the spines on different parts of the axis, e. g. in the same colony 

 they may be arranged irregularly, in linear series and in whorls. In many 



