Reactions of Molosoiria to Chemical Stimuli 47 



siderably extended and spread out on either side. The prosto- 

 mium is spread out and elevated above the plane of the pharynx 

 and peristomium. The pharynx sucks in the algse, bacteria, etc., 

 assisted by the beat of the large cilia or cirri of the buccal cavity. 

 VVlien larger pieces of food are to be swallowed the prostomium 

 and peristomium may be used as lips to envelop the substance to 

 be ingested. 



As an aid in securing food the small cilia of the peristomium 

 beat incessantly from before backwards, drawing currents of water 

 from in front of the animal and washing them against the cirri 

 of the buccal cavity. By testing these currents with fine india 

 ink granules, it was noted that, in the case of a large A. tenebra- 

 rum, the currents began fully 4 mm. anterior to the animal, were 

 drawn past the sensory hairs into the buccal cavity, then were 

 caught and turned to either side by the extended peristomium. 



These currents serve a twofold function. They carry particles 

 of food material into the region of the mouth, and also enable the 

 animal, bv means of sensory hairs, to test the media into which it is 

 moving. These cilia always beat in the one direction. As the 

 animal moves along, the anterior segments of the body are 

 shifted about in all directions by muscular activety. The head is 

 also advanced and withdrawn successively. With these move- 

 ments are seen various foldings or puckerings of the prostomium 

 in which the little sensory bristles seem alternately to be covered 

 over and then extended through the loose enfolding membrane. 

 These associated movements are designated as the "exploring 

 reaction." Similar movements on the part of the flat-worm, were 

 called "feeling movements" by Pearl ('03). At the suggestion 

 ot Dr. Jennings we have decided to classify these phenomena as 

 "exploring reactions" as being less subjective and more appro- 

 priate in this particular field. 



When approaching an unfavorable locality the "exploring" 

 reaction becomes more pronounced, and is usually followed by a 

 quick dart of the head backward and its extension in another 

 direction. These darting movements always follow when the 

 prostomium first comes in contact with any solid substance, or 

 even with the surface film when crawling up the sides of the jar. 



