GEOTROPISM IN PLANARIA MACULATA 83 



during experimentation. ' Unfed ' are those which had been 

 without food for five days or more. 



From these results it is evident that two factors are con- 

 cerned in the distribution of the worms: First, previous history 

 as regards exposure to light, and second, the state of metabolism 

 of the worms in relation to feeding. Both fed and unfed worms 

 which had previously been in the light were found to be mostly 

 positively geotropic immediately after being put in the dark. 

 The fed ones then became negative for a short time. Finally 

 both became indifferent if feeding was stopped. Those which 

 had been in the dark for a long time were negative when fed 

 and indifferent when unfed. Walter ('08) makes the statement 

 that Planaria gonocephala " seems, after several hours of ex- 

 posure to the dark, to be positively geotropic," while Kafka 

 ('14, p. 151) says that Planaria gonocephala is negatively geo- 

 tropic after long retention in the dark. Both of these appar- 

 ently contradictory statements are probably true, since the length 

 of exposure to the dark may very well be an important factor 

 in the geotropism of Planaria gonocephala, as my experiments 

 show for its close relative, P. maculata. 



That this negative geotropism of fed worms in the dark is 

 not in reality a response to oxygen from the open neck is shown 

 by the following experiment. A flask containing 20 planarians 

 was completely filled with water, and the mouth covered by a 

 glass plate. It was then immersed neck downwards in a jar 

 of water in the dark-box. Previous to the experiment the 

 planarians had been fed every other day for two weeks, and were 

 dividing so that at the end of the experiment there were 27 

 worms instead of 20. The per cents found in the three areas 

 of the flask under these conditions were as follows: Top, 58; 

 middle, 33; and bottom, 9. These are of the same order as the 

 last two series of the per cents given in Table I. Table II shows 

 this relationship. 



