CILIARY CURRENT IN PARAMECFA 283 



reveal in specimens swimming freely any evidence of the pro- 

 duction of feeding cones. Under certain conditions such cones 

 are, however, produced in free-swimming animals as will be 

 shown later. 



The currents produced by free-swimming paramecia were 

 studied by fixing the attention upon single particles just in front 

 of them and watching the movements of these particles until the 

 animals had passed. The absolute movement of the various 

 particles is extremely difficult to ascertain owing to the rapid 

 movements of the animal, but certain points come out very 

 clearly. Particles in front of the animals are not set in motion 

 until they are within less than twice the length of the animal's 

 anterior cilia. They are then drawn toward the advancing ani- 

 mal until they are apparently in contact with its cilia when they 

 are thrown rapidly to one side and are carried back along the 

 surface of the animals, those in the oral groove moving consider- 

 ably more rapidly than the rest. The current in the oral groove, 

 however, although stronger, does not draw particles from in 

 front to any greater extent than does that of the aboral side. 

 The more rapid movement of water in the oral groove is com- 

 pensated by lateral movements of the anterior end of the animal 

 resulting in the spiral course, and there is no indication whatever 

 of the formation of a cone. The direction and relative rate of 

 movement of the particles surrounding the paramecia compared 

 with the rate of movement of the paramecia are represented in 

 figure 1. 



In ordinary cover-glass preparations under the monocular 

 microscope the paramecia very frequently appear to draw in a 

 constant cone-shaped stream of water from the front just as 

 has been described for animals which are at rest and are pro- 

 ducing feeding-cones. This may be observed either by placing 

 them in a dilute suspension of India ink or carmine or by adding 

 ink at one side so that it forms a dense, sharp-edged cloud into 

 which the animals swim. Under these conditions, however, 

 the cone is not always produced — many animals approach and 

 enter the cloud of ink without seeming to displace the particles 

 of ink in the least until the cilia on their anterior ends come into 



