THE PROTOZOA 



may underlie all phenomena of protoplasmic contractility, including 

 amoeboid movement and ciliary and flagellary action, as well as muscular 

 contraction. 



Paramecium is propelled in its course by the beating of its thousands of cilia, 

 but their beat is not random. Successive "metachronal" waves of action 

 sweep smoothly along each row of cilia from the anterior to the posterior end 

 of the animal, indicating that the ciliary beat is coordinated by some integrat- 

 ing activity. These waves can be interrupted by making transverse incisions 

 through the ectoplasm of a paramecium; this demonstrates conclusively 

 that the coordinating influences are conducted longitudinally through the 

 ectoplasm. Looking for a structural foundation for these phenomena, we 

 find that the kinetosomes of the cilia are interconnected in longitudinal 

 rows by fibrillar strands, all of which are related to a central ectoplasmic 

 structure near the mouth. It is difficult to avoid the conclusion that the 

 coordination of beating in the rows of cilia is niediated through this fibrillar 

 system, which has therefore been termed the neuromotor apparatus; the central 

 structure from which the strands radiate is called the motorium. 



One further aspect of ciliary action in Paramecium and other ciliates remains 

 problematic. In the "avoiding reaction," to be discussed below, the animal 

 stops and moves abruptly backward for a short distance. This does not, 

 however, involve merely a reversal of the metachronal waves; rather, all the 

 cilia immediately and simultaneously reverse their actions. Investigations of 

 this phenomenon have yielded rather equivocal answers, but it appears 

 certain that the reversal action is not mediated through the longitudinal 

 ectoplasmic fibrillar system. 



The locomotion of Paramecium is a composite of three basic movements: 

 progression, rotation, and swerving. The animal moves forward, rotating on 



Fig. 8.20. Ciliary action. ^-1, outline 

 of a ciliate, showing metachronal 

 waves of ciliary beat. B, phases of 

 action of a single cilium; schematic. 

 £, 4: successive stages in effective 

 stroke; R, 5-12: stages in recovery 

 phase. (Redrawn from K. von Frisch, 

 1952, Biologie, vol. 1, printed by 

 permission of Bayerischer Schulbuch- 

 Verlag.) 



251 



