MOYRMENT.'=!, KTC, OF FRRSH-WATRR PLANARIANS. 633 



feeding' beo'ins is not immediately apparent, but I am inclined 

 to think its pnrpose is to intimately test the snbstance with 

 regard to its availability as food. Some evidence on this 

 point and further discussion regarding ?t will be introduced 

 later. 



After the preliminary pause nnd "gripping" of the food 

 the worm glides up on to it to begin active feeding. The 

 position taken by the worm brings out a ver}^ nice correlation 

 in reflexes. In a ver}- large number of cases (certainly over 

 75 per cent., so far as my observations have gone) the worm 

 advances over the food until the pharyngeal opening is 

 exactly over the place where the tirst "gripping" occurred, 

 and there the pharynx is extruded and feeding begins. 



Fig. 30. — Diai^ram showing great extension of the pharynx. Tlie 

 stippled area represents food substance on wliich the phuiarian 

 is resting. 



When the worm reaches this position the posterior part of 

 the body relaxes and takes on the appearance character- 

 istic of the resting specimen. The pharynx is thrust out, 

 and becomes attached very quickly. As it passes out through 

 the opening in the body-wall it becomes usually considerably 

 extended, and its diameter becomes correspondingly smaller 

 than when it is in the pharyngeal sac. It may or may not 

 attach to the food directly beneath the body. When con- 

 ditions are favourable it usually does, and consequently 

 cannot be seen on looking down on the animal from above. 

 On the other hand, I have frequently seen it stretcluMl out 

 and attached some little distance to one side of the body, as 

 shown in Fig. 30. The stimulus, causing the extrusion of the 



