INGESTION IN THE CILIATE, FRONTONIA 337 



the fiber against the body wall. It will be convenient to desig- 

 nate the points where this occurs as tension points. Specifi- 

 cally, however, the writer would define tension points as those 

 points of contact between the ingested material and the body 

 wall in which a sufficient pressure is exerted to be a stimulus. 

 Such stimuli result in, (a) the changing of the angle between the 

 body axis and the fiber, or in, (5) certain characteristic body 

 contractions. It will be shown later that cyclosis is also an 

 important factor in relieving the stimulation at the tension 

 points, especially when flexible fibers are being ingested. 



When the food fiber comes in contact with and protrudes the 

 aboral wall, special effort seems to be exerted in an attempt to 

 continue ingestion without altering the process. This outward 

 pressure at the tension point seems to serve as a stimulus and 

 to cause one or more things to happen. Sometimes partial 

 or complete ejection of the food takes place, either suddenly by 

 jerky movements, or slowly by reversing the ingestion process. 

 Usually, however, the body of the frontonia goes through cer- 

 tain squirming movements and straightens out more in line 

 with the axis of the fiber, thus aiding in the continuation of the 

 ingestion process, (fig. 4). It will be noted from figures 1 to 8 

 that the frontonia is now turned through an angle of 180° from 

 the position at the beginning of ingestion. When in this position 

 the incoming food meets the least resistance, as the end of the 

 fiber must now travel posteriorly along the aboral wall (5, c 

 and d) rather than anterodorsally, as it did when it first entered 

 the mouth. Thus, at the completion of this stage of ingestion 

 the organism is turned completely around (compare fig. 1 and 8). 

 It will be noted that during the early stages of ingestion the cil- 

 iate is usually directly over the fiber with the anterior end bent 

 downward so that the mouth will come in contact with the end 

 of the food body. This being the case, the end of the fiber which 

 is being ingested is raised from the substratum. 



The turning of the body, as shown in figures 3 to 6, causes the 

 point of contact (fig. 3, a) of the end of the oscillatoria filament 

 and the body wall to shift posteriorly (figs. 4, 5, and 6; h, c, 

 and d). After the body reaches approximately the position 



