354 LOUIS MAX HICKERNELL. 



foot and proboscis. The method of locomotion depends to a 

 large extent upon the temperature and purity of water in which 

 the animal lives. Other things being equal, a relatively high 

 temperature is conducive to active swimming movements, while 

 with lower temperatures the animal generally restricts itself to 

 the leech-like creeping. Another factor influencing the kind of 

 movement is the purity of the water. In cultures which contain 

 many putrefactive bacteria the animals usually are found creep- 

 ing sluggishly about, and they seldom extend the trochal cilia 

 for any great length of time. 



Swimming is the result of the rotating of the trochal cilia and 

 involves no turning upon the body axis. The body movements 

 during swimming are similar to those of certain infusoria as 

 described by Jennings ('04). If any obstruction is met with in 

 swimming the trochal cilia are suddenly retracted and a series 

 of random testing movements occur. The cilia are then ex- 

 tended and swimming is resumed in a direction where there is 

 no obstruction. Sometimes an animal will be observed to stop 

 if it swims through a region where food is abundant. In this 

 case it attaches itself by the foot and feeding movements begin. 



In creeping the rotating organs are always retracted. The 

 animal attaches itself by means of the secretion of the pedal 

 glands and then after a greater or less number of testing move- 

 ments, in which the body is stretched successively in several 

 directions, it attaches itself by the end of the proboscis. This 

 attachment of the head region is followed by the wrenching loose 

 of the foot. The latter is then brought to a point nearer the 

 head and the operation is complete. In changing from the 

 creeping to the swimming movement the trochal discs are ex- 

 tended and the foot is loosened by a contraction of the muscles 

 in the posterior region. The animal then moves steadily forward 

 as long as its trochal cilia are in motion. 



While feeding the animal is always attached by the foot. 

 Currents created by the rotating organs carry bacteria, algae, 

 etc., in a steady stream into the open pharynx where they are 

 further propelled by the long cilia lining the pharynx. The 

 body may sway from side to side during feeding, in fact, the 

 animal is frequently seen to bend its body as if to reach some 



