378 ELIZABETH S. P. REDFIELD 



FUNCTIONS OF THE GRASPING ORGAN 



Certain classes of materials, such as substances suitable for 

 food, call forth in Dendrocoelum a very striking reaction, which 

 involves the grasping organ. If, for example, a pair of forceps 

 which has been dipped in a twenty per cent cane-sugar solu- 

 tion is held in front of a Dendrocoelum, the animal will suddenly 

 dart its head forward and seize the forceps with the grasping 

 organ, and adhere to them so firmly that the creature can be 

 shaken loose only with difficulty. The word ' pounce ' de- 

 scribes this reaction more vividly than any other, and the idea 

 of a pouncing worm can surprise the reader no more than the 

 reaction did the author. 



A moving bait will call forth this reaction more readily than 

 a motionless one. Living Hydra, and pieces of meat are seized 

 by Dendrocoelum lacteum in this manner. These facts suggest 

 that the grasping organ is used to capture and hold the prey of 

 the planarian, until the pharynx can be affixed and feeding 

 begin. To ascertain whether the grasping organ was primarily 

 concerned with feeding, the following experiment was tried. A 

 solution of brown sugar, which was visible in water, was applied 

 by a capillary tube to various regions on the surface of the 

 worm. On stimulating the lateral edges there was a local 

 expansion of the body, a condition to be observed anywhere" 

 between the posterior end and any point almost as far anterior 

 as the auricular appendages. In the neighborhood of these 

 appendages, the application of the sugar solution caused the 

 head to be turned towards the region of stimulation, the grasping 

 organ to seize the end of the capillary tube, and feeding to begin. 



Animals tested in this way with a capillary tube containing 

 only water instead of brown-sugar solution, gave no reaction, 

 and consequently the responses to the sugar solution could not 

 be regarded as due to the mechanical disturbance produced by 

 the slight current of water. From this experiment, it seems 

 clear that the receptors which initiate the feeding reaction of 

 the worm are located upon its head. 



As a further test of this conclusion, the following experiments 

 were made. Worms from which the brain, eyes, and auricular 

 appendages had been removed by decapitation, were put each 

 in a Syracuse watch-glass full of water and left standing twenty- 

 four hours. A twenty per cent brown-sugar solution was then 



