THE MECHANISM OF LIFE 571 



'ying tissue ))(■ excised from a Jlrroe, ii preparation is obtained in 

 a form vnny to study. The movcsment begins in the uppermost 

 plate ;ui(l jiroi^.eds to all the succeeding ones. If the uppermost 

 plate is ;it rest, so an; all the succeeding ones; a plate in the 

 middle of the row never contracts while the preceding ones are at 

 rest. If ;i plate in the middle of the row be held fast, the ciliary 

 waves course from abov;' down to this plate only ; they stop here, 

 and all the lower plates in the series stand still (Fig. 274, ///). 

 Thus every plate is in the closest dependence upon the one next 

 above, and is never able to move independently. But the move- 

 ment of all th(! plates is determined in this manner by the first 

 plate of the seric^s (Fig. 275, A). In spite of this, every plate 

 jiossesses m jioiiewitw ii certain independence. If, e.^r., the row be 

 cut through, tht^ plate that now stands first in the series under- 

 takes the lead, and controls by its contraction and its rest all the 

 plates standing below it, so that the two separated halves of the 



'/^iW^lW^. 



l''in. 27/j.— //, Intact row of uilla Hhowiii^ normal inotiiehrouiHni of boat. The upporrrioHt (loft) 

 ciUum iiian^nirato.t tho rhythm and tho othora follow at tho wamo rato. B, Uowof ciliii dividod 

 in tho iniddlo by a ont. Ifiaoh half actw with ita own rhythm. 



row now act with st'parat-e rhythms (Fig. 275, B). Every indi- 

 vidual plate, indexed, taken out of th(^ seric^s contracts rhythmi- 

 (^ally, ])rovidc(l that the cell-body belonging to it is still present. 

 There is lun-e an interesting case of complete subordination. Every 

 ciliated cell of an epithelium, so long as it is living, possesses in 

 itself coin])lete autonomy as I't'giirds its movement; in union with 

 its like, howevt'i-, it has wholly given uj) the independence of its 

 iiiovi^meiit'. This is necessary if a metachronous motion, which 

 possesses (essential advantages, is to eomt^ about. The same relation 

 is found not only between the individual ciliated (udls of an epithe- 

 lium, but also between the individual ('ilia of a cell. In the latter 

 the same metachronism of bt'at exists in a long row of cilia, as may 

 be seen especially plainly in ciliati'-infiisorian cells. No cilium acts 

 before the one iir(HH'(ling it in the row. If the uppermost one 

 i-ests, the whole series is quiet. Nevertheless, every individual 

 cilium, separated from the olJiers, shows complete independence of 

 movemenl. If, e.g., in Hjtirosldvi'iinii the long row of peristome 



