GEOTROPISM IN PLANARIA MACULATA 



85 



farthest from the supply of oxygen, so that their position was 

 a true response to gravity. 



To find whether the presence of the slime tracks influenced 

 this behavior, indifferent animals were kept for a week (1) with 

 no change of water, but the slime washed out from the flask 

 daily, (2) with change of water daily, but the slime not washed 

 out, and (3) with no change of water and no cleansing of the 

 flask. Table III gives a summary of results. 



TABLE III 



Since the planarians remained practically as indifferent to 

 gravity throughout the experiment as they were before it was 

 begun, the presence or absence of slime tracks probably had 

 little effect on their geotropism. 



The results of these experiments are in line with observations 

 on the stock animals. They usually remain in the shadow under 

 the stones and along the side of the dish. The majority rest on 

 the underside of the stones, but a great many are to be found on 

 the sides of the dish. Immediately after they finish feeding, they 

 glide to the top and move about over the dish. If the water is 

 changed at this time they soon come to rest near the bottom 

 again. If the water is allowed to get foul after feeding, they 

 remain at the top, probably in this case on account of lack of 

 oxygen below. I have been unable to see daily migration such 

 as Walter ('08) observed. 



It would seem reasonable, therefore, to suppose that the 

 collector who finds planarians ventral surface up on the underside 

 of rocks, sees those which have been feeding, while if he looked 

 in other places he might find the unfed ones in any position. 



