MOVEMENTS, V.TC, OF FltRSTT-WATRK PLANARTANS. 635 



of tlio pharynx is that specimens immersed in favonvahle 

 solutions, such as sn^^ar solutions, do not show tliis phe- 

 nomenon. 'IMiat mechanical stimulation alone does not suffice 

 is demonstrated by the fact that planarians pass over and rest 

 on other planarians without extruding- the phai-jnx, althoug'h 

 the consistency of their l)odies is evident!}' much the same as 

 that of the animals used as food. In fact, they will l)e 

 used as food frequently if they ai"e wounded so as to afford 

 the proper cliemicfd stimulus. The stimulation of tlie anterior 

 end of the body by the food seems also to be necessai"y before 

 pharyngeal extrusion takes place. The data on this point will 

 be presented later in connection with operation experiments. 



The appearance of the body on the food is quite charac- 

 teristic. As mentioned above, when the pharynx is extruded 

 forward, movement stops, and the posterior part of the body 

 becomes more or less relaxed. The anterior third of the 

 body, however, keeps in movement during a considerable 

 part of the time the specimen is feeding. The head is waved 

 about from side to side, and touched to the food or the 

 bottom of the dish here and there. It keeps its character- 

 istic extended form to a greater or less degree. A favourite 

 position is for the anterior third or half of the body to lie on 

 the bottom and move about, while the posterior part lies up 

 on the food. This is the position most frequently seen in 

 specimens feeding on a rather small piece of meat. Wiieu 

 the anterior end gets on the bottom it gives every appear- 

 ance, in many cases, of attempting to glide away, and being 

 only restrained by the attachment of the pharynx to the 

 food. In other cases, however, the anterior end remains 

 quiet. The importance of the attempted movement will be 

 brought out later. As has been mentioned above, the flat- 

 worm is able to move off and drag the food still attached to 

 the extruded pharynx along behind it. In the fastening of 

 tiie food to the body in this case the sticky slime undoubtedly 

 assists the pharynx. 



After the food has been softened by the digestive juices, 

 it is taken into the body through the pharynx. 



