7. Anthozoa (incl. Hydrocorallia). A. Zoantharia. . 21 



the animal becomes less hungry the reaction of all parts becomes slower and 

 less precise, the mouth, however, being more ready to respond than the ten- 

 tacles. In a condition approaching satiety food may be accepted or rejected, 

 again accepted and rejected several times before being definitely rejected. 

 Tentacles frequently stimulated lose the tendency to respond, but other ten- 

 tacles instantly respont to the same stimulus, but when the animal is satiated 

 all the tentacles refuse to react. Well-fed A. react much more slowly than 

 hungry ones to simple mechanical stimuli. Anemones show acclimatization 

 and do not respont to stimuli which are repeated at sufficiently short intervals. 

 To the same stimulus repeated many times the anemone reacts first by con- 

 traction, then by turning repeatedly into new positions and finally by moving 

 away. A. lives in crevices in reefs, and in order that its disc may protrude 

 into free water the column is often compelled to assume an irregular form. 

 When removed from its natural habitat it still retains this crooked form. Ex- 

 periments on these lines lead to the conclusion that performance of a certain 

 action involves the assumption of certain structural conditions, these conditions 

 persist in a slight degree even in the intervals between the actions and at a new 

 action they show their influence by causing it to take place in the same way as 

 the former one. This may be called habit. All the usual reactions and their 

 modifications are such as so assist the animal in adapting itself to its environ- 

 ment: the food reactions maintain the metabolic processes, the rejecting reaction 

 keeps the surface clean, the tendency to remain in the dark keeps the animal in 

 the crevices of the rocks where it finds protection for its soft body, and so on. 



Parker ( 2 ) states that the labial cilia of Metridium do not reverse when 

 in contact with carmine, Indian ink, sand, pellets of filter-paper, moistened 

 with sea-water, or with solutions of sugar, quinine or picric acid in sea-water, 

 and do not as a rule reverse to crab-meat from which most of the extractives 

 have been taken. The cilia reverse to dilute crab-meat juice and slightly to 

 a sea- water extract of rubber. Reversal is not due to the osmotic action of 

 the reversing fluid, nor to the anions; it is due to potassium ions, and the re- 

 versal due to crab-meat juice is probably dependent upon some organic com- 

 bination containing potassium. There is no evidence of spontaneous reversal 

 or of reversal through mechanical stimuli. In reversal the propagation wave, 

 as well as the effective stroke, change directions. The reversal only occurs 

 where the stimulus is applied and gives no evidence of involving nervous re- 

 flexes. Although crab-meat juice causes reversal of the labial cilia it does not 

 alter the direction of the ciliary stroke on the tentacles or siphonoglyphs thus 

 showing the extreme differentiation of these surfaces to stimuli. Irreversible 

 cilia are probably asymmetrical in that they consist of a supporting elastic 

 element on at least one side of which contractile material is present. Re- 

 versible cilia are probably more nearly symmetrical, with contractile material 

 on opposing sides of a supporting element, but these two portions of con- 

 tractile material must be regarded as chemically different as one becomes pre- 

 dominantly active in pure sea-water and the other in sea -water containing 

 crab-meat juice or potassium ions. 



Parker ( 3 ) finds that the effective stroke of the labial cilia in Metridium mar- 

 ginatum is not reversed by uric acid nor by creatinine but by creatine; as 

 this latter substance occurs in vertebrate muscle it is probably the effective 

 element in bringing about ciliary reversal when fish-meat is applied to the lips 

 of M. No reversal was obtained with cane sugar, grape sugar, maltose or 

 sugar of milk. Reversal was produced by Witte's peptone, deutero-albumose 

 and asparaginic acid, in these instances, as well as in the case of creatine, it 



