640 RAYMOND PEARL. 



(3) The reception of the food stimulus is a function of tlie 

 head. In other words, the head is the only part of the body 

 capable of receiving very Aveak chemical stimuli. 



(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 have 

 already seen that the sense organs concerned with 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 pharynx and of swallowing are preserved after 

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

 the headless pieces could usually 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 protruded, 

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

 ing this conclusion, I can only say 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 when 

 normally connected with the remainder of the body.^ 



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

 that planarians have a very 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 brought forward in connection with 

 the reaction to chemicals. 



