137 



the canal-aijstem of the fresh-water sj^omjes is caused hy the //a(/c/lar 

 motion of the choanorytes in the fiagelltited chambers. This motton 

 (in normal condition) takes lüace in a sinral- or an undulating- 

 line, naincly in a very rapid succession of waves of small ampli- 

 tude^ passing along the fiagellum from, the base to the top) (Fig. ■~)(Ja, 

 59) ; by which a current of water arises straight through the axis 

 of the flagellar spiral^ and similarly in the direction from base to 

 top, ivhile the ivater flous on at the side of the base {Fig. öGa). 

 Exhaustion causes quite different motions of the fiagellum, uith 

 almormal current of icater {Fig. 50 b-d). The ivhole water-current 

 ivithin a fagellated chamber is of course the resultant of the little 

 currents caused by each flageUum separateUj ; it is rapid and re- 

 gular {Fig. 63). In order that a poiverful and steady current inay 

 be maintained by the chamber, and that, therefore, the water will 

 ■fioiv in quicMy and exclusively at the prosopyles and flow out by 

 the apopyle, the structure of the fiagellated chamber must comply 

 with definite requirements. This structure must be siich that: 



a. the 3 zones, ivhich can be distinguished in a fimctionating 

 chamber, 2«' the zone of negative, 2>td that of iticreasing, 

 3^'d that of positive water-pressure, remain absolutely separated, 

 so that no water can pass from one zone into the other in 

 any other way than from the 1^^ into the 2"^^ and from the 

 2>"i into the 3<-^ zone (Fig. 63). 



and that: 



b. this u-ay of passiyig of the water goes as quicJdy as possible 

 (Fig. 64). 



Finally some separate poiiits: 



The motion of the flagella in the chambers does not change 

 when the ostia close, as I repeatedly statod. 



Besides the above (p. 135) mentioned function of rcgulation 

 of the current, we can probably ascribe to the coUars that of 

 protcction of the flagella against injiiry and mutiial entanglement. 

 A third and much more important function will be treated in 

 the next chapter. 



Finally I should mention that Delage and Héroüard (1G) 



