128 



I say „probably"; for I can only speak of the motion of the 

 flagella of the Spongillidae ; it might be possible, though to me 

 it does not seem very likely, that in other sponges the movement 

 is quite a different one. 



It stands to reason that my observations are not confined to 

 the one given here. I have made many, and all of them with 

 the same result. I shall not describe them again, but I will only 

 give a few illustrations; they speak for themselves (Fig. 57 a — /"). 

 The same for a number of choanocytes still joined within a part 

 of a flagellated chamber (Fig. 58 a — c). 



Always — in favourable conditions of course: the' choanocytes 

 are often immediately damaged — the motion of the fagellum 

 was at first a rapid succession of (spiral-) ivaves of small ampli- 

 tude. The ivaves were moving — without any exception — from 

 the base to the top of the flagelhim; and consequently the water 

 with the particles was pushed on from the cell quickly and in a 

 straight line through the axis of the flagellar spiral^ while it flotved 

 towards the base laterally. One can understand that with such a 

 rapid succession of actions it was not easy to make out, whether 

 the flagellum moved exclusively in one plane, as a flat motion, 

 or as a spiral one; one time it showed a flat wave, next deci- 

 dedly a spiral; however, it does not matter very much. (I will 

 revert to this subject later on.) 



After a short time this regular, rapid motion passed always 

 into a slower, less regular one, during which at first the un- 

 dulating-motion (and the water current) persisted, but this soon 

 ceased, to pass into the still slower and more irregular rowing- 

 motion, by which the water was only stirred a little, and no 

 more pushed away. The end was absolute stopping of the stretched 

 flagellum ; but not always for long. Sometimes (Fig. 57) the mo- 

 vement began again after a quarter of an hour's rest, but very 

 seldom the original rapid undulating-motion (and then only for 

 a few moments), but more the later phases, alternatively, now 

 the rowing-motion (Fig. 57 c?), then the „lash" (Fig. 57 e); and not 

 fluent but jerking, interrupted by periods of rest, and very soon 

 followed by entire stagnation, the flagellum (Fig. 57 /") stretched 



