127 



the particles is at first stirred to and fro, but finally 



pushed away in upward slanting direction (Fig-. 56 c). 



6.10 p. m. The last movement (Fig. 56 c) was evidently a 



transition from the spiral- or undulating-motion to 



this new one: A slow ') beating to and fro of the 



ftagellum, without ivaves. The water ivith the particles 



is moved to and fro^ hut it is not pushed away (Fig. 56f?). 



6.15 p.m. The ftagellum stops in a more or less straightened 



condition (Fig. 56e). 



To this I must add that after the phase, given in Fig. 56 a, the 



motion of the flagellum became less regular; it was interrupted 



by resting-periods of unequal, but ever increasing length till 6.15 



p. m., when it stopped finally. There was no collar to be seen in 



this choanocyte, evidently it had been retracted. 



One will acknowledge, now, that the first phase (Fig. 56 a) of 

 the flagellar motion is in fact quite different from that which 

 the investigators have hitherto observed. It goes without saying 

 that the water current caused should prove quite a different one 

 also. But there is still more to be seen in the figures: the mode 

 of motion of the flagellum, hitherto described (by Bowerbank, 

 Lendenfeld, Cotte^ Vosmaer and Pekelharing), fully agrees 

 with our phase given in Fig. 56c? — even the current of water! 

 Now, the phase of Fig. 56 d however is quite abnormal, and caused 

 by exhaustion, as after 5 mnts. it is already followed by final 

 stagnation of the flagellar movements. The explanation, why these 

 last phases (Fig. 56 c, cZ), the rowing-movement, have always been 

 found by the investigators and never the first one (Fig. 56«), the 

 screw- or undulating-motion, is quite clear now. Moreover, I will 

 just call attention to what Bowerbank said, as I quoted already 

 on p. 121 : „When in vigorous condition their motions" (of the 

 flagella) „are rapid and cannot readily be followed, but in 

 some in which the action was languid" etc.! Prohahly one 

 has always observed the movements of more or less exhausted flagella. 



1) That is to say, comimrcd with the former intense motiou; it still goes rather 

 quickly. 



