Selection of Food in Stentor Cceruleus (Ehr.) 83 



The most conspicuous of these cihary appendages are of course 

 the membranellae, which are inserted around the rim of the disk. 

 Their normal action creates the well known alimentary vortex by 

 means of which a constant stream of water is caused to flow against 

 the disk. In this manner the Stentor procures whatever small 

 particles there may happen to be suspended in the water. The 

 particles as well as the water in which they are suspended are 

 driven against the disk more or less perpendicularly. The water 

 is driven out over every part of the rim of the disk, while the par- 

 ticles striking against the disk are carried slowly b) the discal cilia 

 toward the pouch. The transportation of the particles on the 

 disk is not due to any feature of the movement of the mem- 

 branellae, butisentirelydue to the discal cilia. These are very small 

 organs and are disposed in rows more or* less parallel to the mem- 

 branellae. Their action cannot be observed except under the high 

 power of a compound microscope. Their arrangement, size, etc., 

 can then also be seen. The particles, as they strike the disk, are 

 taken by these cilia and slowly passed on in the direction of the 

 pouch, over the rim of which the particles are dropped. The par- 

 ticles are then taken by the pouch and funnel cilia and either 

 passed down to the mouth, where they are ingested, or else are 

 swept out over the rim of the pouch on the ventral side of the Sten- 

 tor. The cilia of the pouch and funnel are considered as of one 

 system because their functions are identical as far as can be deter- 

 mined. It has been found impossible to observe just how these 

 cilia beat under various conditions. It is of course quite certain 

 that when a particle is ingested they beat downward toward the 

 mouth, and that when a particle is rejected they beat in the oppo- 

 site direction. It is also found that a small particle in the center 

 of the pouch is httle acted upon by the cilia, but as it comes nearer 

 the cilia it begins to travel faster. It is probable therefore that 

 the transfer of particles in the pouch and funnel is effected more 

 by actual contact with the cilia than by mere transportation in a 

 current of water which is set in motion by their action, and this is 

 probably true also for the action of the discal cilia. Only small 

 particles are wholly transferred by the action of the pouch and 

 funnel cilia. Large particles, such as paramecia, are ingested 



