1072 



Clioanoflagellates. We see at once that this must necessarilj be the 

 case of fig. 2, the diagrammatic representation of tlie water-current 

 in a fiagellated chamber as the resultant of the smaller currents 

 caused individually by each flagellum. For the bodies and collars of 

 the choanocytes must as it were filter the water, circulating between 

 them, free from floating particles. A representation of the way followed 

 by the food-particles from an incurrent canal through the prosopyles 

 inside a flagellated chamber is seen in fig. 3; it was drawn from 

 the living object, but diagrammatized as regards the choanocytes-layer. 

 It is seen that the particles — as is generally the case — - pass by 

 the layer of choanocytes (evidently this layer is too compact and 

 the open spaces between the cell-bodies do not admit of a vigorous 

 circulation of water). At the level of the bases of the collars the 

 particles however immediately deviate aside, to be soon captured 

 — still at the bases of the collars. 



I established that the food-particles are next taken up within the 

 choanocytes, to be fairly soon expelled by these again into the 

 mesogloea; a phenomenon that 1 have also been able to observe in 

 my living preparations. Finally (lie particles reach the amoebocytes, 

 which probably have taken them up out of the mesogloea. 



In addition to this method of capture by the choanocytes of — 

 what I found to be almost exclusively small — food-particles, I was 

 able to observe yet a second method of ingestion — of coarser 

 particles — not within the flagellated chambers. That this method 

 should exist was indeed to be foreseen. For the width of the ostia 

 in living fresh-water sponges may be, according to my measurements, 

 even 63 X 84 n, whilst the prosopyles usually only measure 3 — 4 ft. 

 It is therefore obvious, that with the current of water there will 

 enter by the ostia numerous particles, which are too large to pass 

 the prosopyles. These particles would therefore threaten to stop up 

 permanently all the |)rosopyles of a sponge, if the latter had no 

 means at its disposal of removing them again. 



The sponge is indeed furnished with very efficient means, as 

 I have observed in my living microscopic preparations. It is known, 

 that the choanocytes-layer of the flagellated chambers is covered on 

 the side of the incurrent canal with a thin layer of tissue. When 

 living, this layer proved to me to consist of apparently undifferen- 

 tiated protoplasm (up to about 3 ix in thickness), and to be simply 

 continued from the lining of the incurrent canal over the flagellated 

 chamber. In it I observed all ^orts of corpuscles, such as oil-droplets 

 or food (carmine) particles caught by the choanocytes, being very 

 often slowly carried on by protoplasm current, and so displaced 



