132 



ments. Is this in fact a spiral, or is the whole wave in one flat 

 plane? It could not be made out very well in the isolated choa- 

 nocytes; but all the better in the intact flagellated chamber. For 

 there we see, as I said before, a number of collars from above on 

 the top (as a circle), the flagellum within (as a spot) (Fig. 60). It 

 then proves that that spot — the section of the flagellum — 

 usually describes a flat ellipse or an almost straight line (Fig. 61, 62); 

 consequently, that the flagellum itself performs its undulating- 

 motion either as a flat spiral or in one flat plane. (As above 

 mentioned, this makes but little difl'erence to the effect on the 

 water). 



So we have shown definitively that the normal flagellar motion 

 of the choanocytes is : a very rapid succession of (spiral- Jivaves of 

 small amplitude, Sfoing on from the base to the top of the fla- 

 gellum (Fig. 56 a, 59) and causing a current of water straight 

 through the axis of tJie flagellar spiral also in the direction from 

 base to top, while the water flows laterally towards the base. Ex- 

 haustion causes wholly different flagellar motions with abnormal 

 current of water. 



The water-current caused by all the flagella together in a fla- 

 gellated chamber must of course be the resultant of all the little 

 currents, caused by each of the flagella separately. We have got 

 to know the current of water during the normal motion of the 

 flagellum of the isolated choanocytes (p. 126 — 128). Within a 

 flagellated chamber the current of water, caused by each flagellum, 

 must, as the mode of moving of each flagellum is the same, 

 necessarily be equal to that which the flagellum would show in 

 isolated condition of the choanocyte; so here there must be again 

 for each flagellum a current of water through the axis of the 

 flagellar spiral away from the cell, so now directed towards the 

 centre of the chamber, while the water flows on towards the 

 base of the flagellum laterally (Fig. 58a). The whole water-current 

 within the flagellated chamber, as the resultcmt of all little currents 

 caused by each flagellum separately, can be made clear in the best 



