640 KAYMONP PFAnr,. 



(3) Tlie reception of the food stimnlns is n function of the 

 head. In other Avords^ the liend is the only part of the body 

 capable of receiving very weak chemical stimnli. 



(4) Decapitated specimens do not extrude the pharynx, so 

 far as my observations go, even though the proper normal 

 stimuli are given the pharyngeal region. Presumably the 

 brain is the necessary organ in this connection, as we liave 

 alread}^ seen that the sense organs concerned witli the act of ex- 

 trusion are not those of the head, but of the pharyngeal region. 



Bardeen (: 01, a, p. 178) states that ''the simple reflexes of 

 extending the pharj-nx and of swallowing are preserved after 

 removal of the head. I found, by repeated trials, that one of 

 the headless pieces could usuall}^ be made to eat if it was 

 placed on its back on a slide in a small drop of water. Under 

 the conditions mentioned the pharynx is usually piotruded, 

 and will engulf bits of food placed in the mouth." Regard- 

 ing this conclusion, I can only sny that in a large number of 

 experiments with decapitated specimens I have never been 

 able to induce extrusion of the pharynx, under conditions 

 approximating as closely as possible to the normal. I do not 

 wish to affirm that the decapitated planarian cannot extrude 

 the pharynx, but merely that it does not when placed in 

 situations which normally produce pharynx extrusion. 



(5) The pharynx is not an independent organ in its reactions, 

 since, when separated from the body, it does not react with 

 reference to the localisation of the stimulus, as it does wIumi 

 normally connected with the remainder of the body.^ 



2. Summary of Food Reactions. — It is shown above 

 that planarians have a veiy definite and characteristic set of 

 reactions to food substances which enable them to become 

 aware of the presence of food, and find it. The importance 

 of these reactions in the life of the individual can hardly be 

 over-estimated. While planarians, like many other lower 

 organisms, can live for a considerable time without food, yet 

 in the long run they must, of course, have it. The question 



^ Evidence on this latter point will be biouglit forward in connection with 

 tlie reaction to cliemicats. 



