123 



of the sponge on a thin-walled Leucosolenia, a tube-like calca- 

 reous sponge, the inside of which is entirely covered with choa- 

 nocytes. I will quote now: „A piece of about 1 cm. was cut from 

 a tube and then split open and immediately observed. The piece 

 was covered with a cover-glass ; but this could hardly harm the 

 choanocytes, as it was carried by the apical rays of the tetra- 

 scleres. The preparations were observed with Zeiss's homog. imm. 

 1.40, 3; Oc. 12, It was evident then that the flagella were beating 

 quite independently from each other, all in different directions" 

 (as Fig. 56 (^, bid, 58 i). „The movement of each flagellum was 

 not always in the same plane, and one moment it was stronger 

 in one direction, another moment stronger in another. Sometimes 

 a flagellum was stretched for a while almost horizontally. It 

 happened also that one or more flagella were motionless, in order 

 to beat again vividly a few moments afterwards. Every now and 

 then flagella crossed, without ever becoming entangled. Particles 

 suspended in the water were whirling about, never carried for- 

 ward. In short, the aspect of the motion was absolutely different 

 from what is observed in ciliated membranes of higher animals. 

 There was no trace of a coordination of neighbouring cells". 



The authors continue : 



„. . . . this mode of motion cannot be but advantageous for 

 capturing particles by the choanocytes. This is not only the case 

 for choanocytes forming flagellated chambers, but eminently so 

 for those lining the cloacae of Leucosolenia. If all the flagella 

 lashed briskly towards the osculum, the particles, entered through 

 the pores, would be directed chiefly towards the axis of the tube 

 and rapidly removed through the osculum. On the contrary the 

 movement of the flagella has the effect that particles can easily 

 reach the collars and thus come into contact with the protoplasma 

 of the choanocytes". 



„Moreover it seems possible to us, to explain by the irregular 

 motion of the flagella, the regular current through the canals of 

 the sponge, as this is so often observed, and so carefully studied 



by Grant it seems to us that in the living sponge the 



water would find more resistance in flowing out from the chamber 



