48 H. G. Krihs 



If the object is not harmful the prostomium may be returned and 

 thus touch the object two or three -times until a certain "familiar- 

 ity" is established. The animal then moves over about the 

 object without further retardation. If the object should be 

 injurious the backward move is vigorous, the head is thrust 

 energetically in another direction, and a general movement away 

 from the scene of contact is made. Sometimes the avoiding 

 movement is so energetic that the dart backward and toward one 

 side are practically simultaneous. In this case there is usually a 

 compensatory movement of the posterior segments in the opposite 

 direction from that of the prostomium. At other times the action 

 of the head may be entirely reversed by the violence of the move- 

 ment and the animal will glide directly away from the unfavor- 

 able region. This movement is well illustrated when the prosto- 

 mium comes in contact with one of the tentacles of a hydra. 



The locomotor movements of ^olosoma while feeding are of a 

 slow crawling nature. The beat of the cilia under the prostomium 

 seem to play no part in them. Progress is made by means of 

 successive alternate contraction and extension of the muscles of 

 the body segments. In this wav the ^^olosoma may move back- 

 ward or forward. In the more rapid of these movements the 

 pharynx and papillje are alternately stuck to the sub-stratum 

 while the other end is advanced or retracted. This movement 

 may be so vigorous as to resemble the looping of a "measuring" 

 worm. 



There is generally associated with the feeding reaction a cer- 

 tain peristaltic movement of the body wall which is entirely in- 

 dependent of the movements of the digestive tract. The wave 

 begins in the region of the pharynx and runs backward to the end, 

 slightly elevating the several bundles of setae as it passes through 

 them. There is no evident shortening or elongation of the body 

 during the process. The waves follow each other in rhythmical 

 succession at brief intervals. They may vary in size within rather 

 wide limits. They are more vigorous about the time of the exci- 

 sion of a zooid from the parent. As constriction proceeds there 

 is a noticeable "twitch" as the peristaltic wave passes from the 

 parent to the zooid owing to the imperfect muscular connection 



