THE CHEMICAL SENSE OF NEREIS VIRENS. 



237 



form of behavior which may be described as a rhythmic un- 

 dulatory movement of a portion of the body taking place in a 

 dorso-ventral direction, the parapodia remaining passive. These 

 muscular waves were sometimes limited to the anterior end, in 

 which case a nodding of the head occurs ; at other times they 

 appeared only at the posterior end, or perhaps in a position 

 nearer the middle of the body. The movement is not uninter- 

 rupted but never discontinued for any length of time. This 

 activity produces a current in the water which passes along the 

 animal's body from the anterior to the posterior end. 



That these body movements also occur when the animals are 

 in their burrows was clearly demonstrated by two individuals 

 kept in glass dishes containing sand. In one instance the nod- 

 ding of the head mentioned above was seen through the glass as 

 the animal lay in its burrow at the side of the dish. Carmine 

 grains dropped in the water a few centimeters above an opening 

 of the burrow 7 were immediately drawn inside. In another 

 case a long burrow was formed against the glass and here the 

 undulatory movements of the worm were distinctly visible. 

 From this burrow three tunnels led to openings at the surface 

 close to the glass. From this it is clear how Nereis, concealed in 

 its passageways within the sand, receives not only a constant 

 supply of fresh water but also may be stimulated by any chemi- 

 cal change in the water above. 



Worms occupying glass tubes respond to chemical stimula- 

 tion of food as readily as those in burrows. Sea water squirted 

 from a pipette close to a tube results in no response, but when 

 a filtered extract of clam is introduced in the same manner the 

 worm starts forward, moving quickly toward the end of the 

 tube toward the juice, thrusting out its head and seizing a bit 

 of clam dropped near the tube, or held in the forceps. This re- 

 action was observed many times and with several individuals, 

 and appears to be subject to remarkably little variation. By use 

 of the glass tube every movement of the worm can be seen per- 

 fectly, and the method promises to be an excellent one for the 

 study of the distribution of the receptors involved in the re- 

 sponses. Experiments designed to throw light on this aspect of 

 the problem are already under way and will be reported upon 

 at a later time. 



