1 

 THE CHEMICAL SENSE OF NEREIS VIRENS. 235 



of the burrow and then withdrew. The same reaction was 

 repeated a few minutes later. Finally at 10:07: 30 it was found 

 with its head exposed directly beneath the clam to which point 

 it had burrowed, a distance of 7 cm. 



Worm II. It repeated its first appearance at the edge of the 

 dish, withdrawing quickly each time. At its third appearance 

 the worm proceeded directly toward the clam, exposing about 

 10 cm. of its body, and then quickly disappeared within its bur- 

 row. At 9 : 59 it came out of the sand 2 cm. nearer the clam, 

 stretched out until it reached the clam, but finding a small frag- 

 ment nearby, it seized the fragment and withdrew without dis- 

 turbing the clam. At 10:07:30 the worm again emerged, this 

 time within 2 cm. of the clam, which it grasped and dragged a 

 distance of 3 cm., partially burying its prize in the sand. When 

 the clam was dislodged the head of worm I. was disclosed 

 directly beneath. At 10:13:30 worm II. reappeared at the 

 mouth of its original burrow at the edge of the dish but made no 

 effort to reach the clam. 



Worm III. Emerging first at the edge of the dish it im- 

 mediately moved toward the clam, not quite reaching it. After 

 withdrawing it came out again at the same point at 10: n, but 

 by this time the clam had been pulled 3 cm. away by worm II. 

 It drew back into its burrow and was not seen again. 



Worm IV. When first noted at the edge of the dish the 

 worm made a few wavering movements and then disappeared, 

 coming up again for a short time 3 cm. away. Finally at 

 10: 17:30 it was observed at the edge of the dish, but 10 cm. 

 from the first opening. It advanced directly toward the clam, 

 seized it but failed to move it because of the position in which 

 it had been wedged in the sand by worm II. After tugging at 

 it a while, and probably biting off a piece, the animal with- 

 drew. 



The results of this experiment and two others carried out in 

 the same way confirmed beyond question our observations made 

 in the field. Although a worm on coming to the mouth of its 

 burrow usually advanced the anterior end of its body in a direc- 

 tion toward the clam, it perhaps showed somewhat less certainty 

 in this phase of its response than when in its natural environ- 



