270 EXPERIMENTAL PHYSIOLOGY 



creeping? Are any muscular movements observable during creep- 

 ing which may account for locomotion? (To be observed under (2) 

 above). Can ciliary action account for locomotion? Notice the 

 movements of the auricles, the triangular projections lateral to 

 the eyes. Is there ciliary movement? Test with powdered carmine. 



With a hair or other delicate instrument explore various regions 

 of the body for sensitivity to touch and determine the order of 

 sensitivity. Touch the tip of the head with a blunt needle. If done 

 carefully the planarian will grip the needle and can be lifted through 

 the water. Response to touch is called thigmotropism, positive if 

 the organism moves toward the source of stimulation or remains 

 attached to it, negative if the organism turns or moves away. If there 

 is no response the organism is said to be indifferent to that stimulus. 



Stereotropism. Do planarians collect in cracks with as much 

 of their bodies touching the dish as possible? 



Chemotropism. Place a small bit of liver an inch or so away 

 from a shaded quiescent planarian. Describe movements of animal 

 in finding the liver, and during ingestion of food note action of 

 pharynx. Is there any circulation of ingested food? 



Geotropism. Do you find any difference in response to gravity 

 depending on whether the animal is fed or not? Be careful to rule 

 out any effect of light. (Olmsted, Jour. An. Behaviour, 1917). 



Galvanotropism. Are the planarians forced to travel to the 

 anode or cathode? Explanation? 



Rheotropism. Do planarians move up or down stream in a 

 gentle current? 



Phototropism. Place five worms in a dish one half of which is 

 shaded, the other half brightly illuminated. Make five trials and 

 note where the worms collect after five minutes. Are they nega- 

 tively or positively phototropic? Use coloured glass over the 

 illuminated half, e.g., blue, red, green, yellow. Differences in 

 response? Throw a narrow shadow down the middle of the dish 

 and start a planarian moving toward the source of light. Can you 

 make the animal continue to move in this direction? Describe 

 movements. Cut a worm's head off just behind the eyes. Describe 

 the responses of each piece to the light. Are the ey/^ essential 

 for the light response? (Consult article by Taliaferro in Jour. 

 Expt. Zool. 1921). 



