MOVKMKNTS, ETC., OF FRES[T-WATER PLANARFANS. 523 



''Excretion is carried in part through the intestines by the 

 act of defecation ; in part it is doubtless carried on by an 

 excretory system opening on the sui'face." A more detailed 

 discussion of various points raised by Bardeen will be entered 

 into in connection with the parts of this work on which they 

 have direct bearing. 



A second paper by the same author (Bardeen^ : Ola) 

 describes briefly the normal food reactions of Planaria, and 

 shows that a decapitated specimen will not find food materinl 

 in a dish, although one such a specimen could " be made to 

 eat if it were 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." An experiment was performed in which the pai't 

 of the head in front of the eyes was cut off. Such specijnens, 

 from which merely the tip of the head had been removed, re- 

 acted normally to food. It is also shown that specimens 

 fi'om which the part of the body posterior to the pharynx has 

 been removed feed like normal worms. Regarding the 

 method by which planarians find food in their immediate 

 vicinity, Bardeen says (p. 176), ''It is difficult to determine 

 the source of the impulse which gives rise to this purposeful 

 activity. It is possible that the auricular appendages here 

 act as delicate organs capable of stimulation by slight 

 currents in the water set up by the minute organisms that 

 prey at once upon the flesh of the dead snail." Experiments 

 to be reported in the course of the present paper show, I 

 think, that the mechanical and chemical stimuli given by food 

 are the ones which affect planarians. 



c. Material. 



The following species have been principally used in this 

 study : — Planaria maculata, Leidy ; Planaria gono- 

 cephala, Duges ; Planaria dorotocephala, Woodworth.^ 

 Of these P. dorotocephala and P. maculata have been 



' Excellent figures and descriptions of lljese three species have been pub- 

 lislied by Woodwoitli, '97. 



