REACTIONS OF PLANARIA TO WATER. 113 



nature. Specimens were kept in large numbers in glass and 

 galvanized iron containers which were emptied of water, rinsed 

 and filled with fresh tap-water from time to time without re- 

 moving the worms which cling to the surface of the vessel. 

 They were fed two or three times a week with fresh beef cut 

 into small bits and left in the dish for several hours or during 

 the night. These worms collect on fresh meat and secure blood 

 and juices but it is very improbable that they are able to make 

 use of the solid portions. 



Rheotropic reactions were tested in a "circular current" as 

 follows: A considerable number of specimens, sometimes several 

 hundred, were placed in a circular shaped vessel such as a glass 

 battery jar or a kitchen pan and the water was stirred vigorously 

 around the dish several times with a stirring rod. Vigorous 

 stirring usually dislodged the most of the specimens which were 

 then swept into a bunch at the center of the current. If they 

 were not dislodged by the stirring, they were loosened by means 

 of more vigorous streams of water from a large bulbed pipette. 

 The movements of the animals on the bottom of the vessel only 

 were studied since those on the sides were in a different relation 

 to gravity which introduced a geotropic factor into the reaction. 

 Rheotropism has been observed, however, in worms gliding on 

 vertical surfaces. 



It was found convenient to have all the specimens, or the 

 larger part of them, enter the experiment at the center of the 

 "circular current" since they were then all placed under similar 

 conditions. In whatever direction any worm started out from 

 the center, it would receive the current against the same side of 

 the body as all the other worms starting from the center. If 

 the current were stirred in the clockwise direction, for example, 

 all the worms starting from the center of the dish would receive 

 the current against the left side of the body. If they gave a 

 positive reaction, they turned toward the left side; that is, 

 toward the side stimulated, or up-stream, and if they gave a 

 negative reaction, they turned toward the right side; that is, 

 away from the side stimulated, or down-stream. When a large 

 number of worms were gliding on the bottom of the dish, if their 

 reactions were uniform, a very striking figure was produced. 



