546 Comparative Animal Physiology 



explanation in terms other than that of a reversal of the direction of beat 

 of individual cilia. The apparent reversal on the labial palps of Ostrea^^ 

 and probably also in the gullet of the coelenterate, Actinoloba,^-^ appears 

 to be explicable in terms of opposite directions of beat of cilia of longitudinal 

 grooves and ridges, together with muscular movements making one or the 

 other of the tracts dominantly influential. 



The cilia of the lips and gullet of the sea anemone, Metridiwn, and also 

 other species of anthozoans, whose tentacles are too short for successful 

 transport of food to the mouth, appear capable of reversal of beat in re- 

 sponse to direct stimulation by chemical agents. In the normal unstimulated 

 anemone the cilia beat outward. When, however, a piece of food material 

 such as crab flesh is brought into contact with the ciliated epithelium, those 

 cilia in the immediate region of the food reverse their beat, now carrying 

 the food into the gullet. Immediately following passage of the particle the 

 cilia resume their outward beat. 



The effect of crab flesh in inducing ciliary reversal in the Metridium can 

 be imitated through the application of 2^^ per cent KCl in sea water or the 

 addition of glycogen, ^'^ etc. After this treatment the direction both of the 

 effective stroke and of the metachronic wave is reversed. Such treatment 

 does not reverse the direction of beat of the cilia of the tentacle or siphon- 

 glyphs. 



In Paramecium ciliary reversal is effected by treatment with KCl and 

 salts of other monovalent cations.^^- ^- When the animal is subjected to an 

 electric field, there is a reversal of beat of cilia on the end of the animal 

 nearer the cathode. 



The only seemingly genuine instance of ciliary reversal in higher meta- 

 zoans appears to be in the ectodermal cilia of amphibian larvae.''" Here local 

 ciliary reversal is observed in response to mechanical stimulation. In all 

 other carefully studied ciliated epithelia in higher metazoans, reversal is 

 apparently impossible. 



Ciliary Control and Coordination. Cilia appear to show a well developed 

 automaticity. The cilia of ciliated epithelium of even small areas of the tissue 

 continue to beat after removal from the organism. In protozoans the cilia of 

 even small fragments of an individual will continue to beat for some time, 

 even in the absence of any nuclear material. Sperm cells with the head re- 

 moved continue to show active locomotion. Such observations indicate that 

 the automaticity of ciliary action resides entirely in the cilium and an im- 

 mediately adjacent region of the cell. A number of observations suggest that 

 an organic connection with the basal granules is essential to the beat. Sep- 

 arating the middle piece from a sperm tail or stripping away the surface of 

 a ciliated epithelium in such a manner as to break the connections be- 

 tween the cilia and the underlying layer of basal granules is re- 

 ported to result in an immediate cessation of ciliary beat.-" It is not 

 yet fully established whether it is the basal granules themselves or some 

 other functional elements in the same general area which are essential for 

 normal activity. 



The cilia of any ciliated surface exhibit through their metachronism evi- 

 dence of the presence of a general coordinating mechanism. Metachronism is 

 a term applied to the characteristic beating of the cilia in any ciliated epithe- 



