634 RAYMOND rFAKT,. 



pliarynXj is the contact of food or other solid body with tlie 

 pharyngeal region of the ventral surface, together with an 

 appropriate chemical stimulus. The pharynx is not extruded 

 until the animal gets up on to the food so that the opening' of 

 the pharyngeal sac is in direct contact with it. This can be 

 demonstrated by direct observation by the use of a very 

 small piece of food material and a plane mirror placed 

 beneath the glass dish in which the specimen is moving. By 

 lifting gently the posterior end of the body on a needle it can 

 also be seen that the pharynx is not extruded before it is over 

 the food. The most striking illustration of the correlation in 

 the reaction which brings about the extrusion of the pharynx 

 when it is just over the food, is to be seen when a specimen 

 of the nemertean Stichosterama asensoriatum is used as 

 food, and the long axis of the planarian and of the nemertean 

 are at right angles to each other. After first " gripping " 



Fig. 31. — Diagrammatic Icngiludinal sccHon of a planarian feeding 

 on a nemertean (shown in cross-section at x ). 



the nemertean the planarian glides along over it until the 

 pharyngeal opening is just above it, and then pauses, and the 

 pharynx is extruded and attached (« and h, Fig. 31). These 

 facts strongly indicate that the effective stimulus for pharyn- 

 geal extrusion is received, at least in part, in the pharyn- 

 geal region itself. That it is necessary for both contact 

 and chemical stimuli to act to produce the extrusion of 

 the phaiynx may be shown by experiments on specimens 

 gliding on the surface film ventral side uppermost. If, with 

 such a specimen, a chemical known to produce under other 

 conditions extrusion of the pharynx, is allowed to come in 

 contact with the pharyngeal region, there is no result. Of 

 course in performing this experiment proper precautions 

 were taken not to disturb the animal by allowing the solution 

 to drop upon it. Another demonstration of the same fact that 

 a chemical stimulus alone does not suffice to cause extrusion 



