Figure 133. — Diagrammatic reconstruction of the distal 

 portion of the ciliated cells of the gill epithelium of C. 

 virginica. ax.f — axial filament; b.pl. — basal plate and 

 basal corpuscle; c. — cilium; c\v. — plasma membrane; 

 mit. — mitochondria; r. — rootlet. Cross section of the 

 cilium shown at upper left corner. 



wanting, that the pair of a.xial fihinients gives the 

 ciHum the necessary rigidity but does not partici- 

 pate in tlie movement. 



METACHRONAL RHYTHM 



Automatism is a general characteristic of ciUary 

 motion. This typical property of ciliated epi- 

 thelium, common to all animals which have 

 ciliated cells, is a fundamental characteristic of 

 the ciliary motion of lamellibranch gills. As 

 Gray (1928, p. 4) stated: "There can be little 

 doubt that all cilia are fundamentally automatic 

 in their movement and that the power possessed 

 by organisms to inhibit the locomotion of their 

 cilia is of extraneous nature." 



In any ciliated surface there is some sort of 

 coordinating mechanism that manifests itself in 

 the metachronal rhythm of the beat. The term 

 metachronal rhythm or metachronism denotes the 

 regular sequence of ciliary motion in which any 

 cilium in a given series is slightly out of phase 



with the ciliiun behind and in front of it. Since 

 the cilia in one row of the epithelium beat at the 

 same rate but are in different phase, their com- 

 bined movement gives the optical appearance of a 

 wave passing over a wheat field on a windy day. 

 The beating of the lateral cilia along the isolated 

 filament of an oyster gill is an excellent object in 

 which to observe the metachronal wave. In the 

 drawing of an exposed surface of the giUs of a live 

 oyster examined under a compound microscope 

 (fig. 134) the metachronal waves along the two 

 rows of the lateral cilia move in opposite direc- 

 tions. The effective stroke of the lateral cilia in 

 this case is at right angles to the direction of the 

 metachronal wave (i.e., perpendicular to the plane 

 of the drawing). The crest of the wave includes 

 the cilia that are ready to begin their effective 

 stroke; in the troughs are the cilia that are about 

 to start the recovery stroke. 



The direction of the metachronic wave is not 

 disturbed by the temporary cessations caused by 

 such extraneous agents as narcotics or cold. 

 Upon recovery the metachronic wave proceeds in 

 the same direction as when the motion was 

 artificially stopped. In the ciliated epithelium of 

 the roof of a frog's mouth the metachronic wave 

 is not disturbed even if a piece of epithelium is 

 cut off and then placed back after rotating it 180° 

 (Briicke, 1917). Transplantation of the gill 

 epithelium of an oyster was tried in the Bureau's 

 shellfish laboratory without success. Copious 

 discharge of mucus, continuous bleeding of the 

 wound area, and the cm'ling up of the filaments 

 interfered with the implantation of the excised 

 pieces. In all my experiments the host animals 

 discarded the implants in a short time. 



The fact that small pieces of ciliated surface 



Figure 134. — Two tracts of the lateral cilia of C. virginica 

 along the two filaments on both sides of the ostia. 

 Small black particles suspended in water are drawn into 

 the ostia while the large ones are discarded by tlie 

 recovery strokes of the lateral cilia. Drawn from life. 



136 



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