Reactions of Molosoma to Chemical Stimuli 49 



between the two. It is during one of these twitches that separa- 

 tion is finally aftected. 



If the food becomes scarce in the immediate neighborhood 

 iEolosoma may ghde or swim to other regions in a way similar to 

 the ghding movement of a triclad. In this case, the ciha under 

 the prostomium are the only organs of propulsion. The body is 

 somewhat extended and straight. The peristomium is with- 

 drawn so as to be practically invisible. The cilia under the pros- 

 tomium seemingly beat more rapidly than before and propel the 

 animal forward. The setae are turned to a sharp angle caudad. 

 Movement is always forward and may attain a speed of 5 mm. 

 or more per second. All changes in directions are made by rota- 

 tion of the head by exercise of the muscles of the pharyngeal 

 region. When iEolosoma settles down after gliding or swimming 

 the posterior segments are generally the first to come in contact 

 with the substratum. Swimming in the open may also be stopped 

 by a quick forward thrust of the seta-. This may be vigorous 

 enough to stop all forward progress or to even throw the animal 

 slightly backward. 



When j^Eolosoma comes to rest where currents r)f water are 

 flowing, its position is maintained by gripping the substratum 

 with the pharynx in a way similar to the suction disc of a leech, 

 as noted by Beddard ('88), or more generally, bv sticking to it by 

 means of the caudal papilla?. When feeding, under such condi- 

 tions, the papillae only are used, changes in position being made 

 by looping. 



The ^olosoma show a great tendency to burrow in the ooze 

 at the bottom of the jar. The prostomium is narrowed laterally 

 and extended somewhat in front and then thrust downward into 

 the sediment. Progress is made by means of a rapid spiral twist- 

 ing movement of the body. 



In the performance of all these movements the animals secrete 

 considerable mucus. The mucus entangles large numbers of 

 bacteria and algae which are caught up as the animal moves about. 

 For this reason the ."Eolosomea will frequently twist aboutand 

 browse over the mucus Aim surrounding the major part of the 

 body, or apparently feed anewon old excreta. They are attracted 



