236 MAN ION COPELAND AMD H. L. WIEMAN. 



ment. This, however, was to be expected, for in the dish well 

 defined water currents bearing" food juices, which undoubtedly 

 aid under natural conditions in directing the animal toward the 

 food, were largely absent, and the stimulating material must 

 have become rather generally distributed through the water. 

 The animals, nevertheless, after stimulation, instead of confining 

 their activities to the periphery of the dish, near which they 

 usually appeared, exhibited a marked tendency on failing to 

 reach the clam to move toward the center of the dish. The ex- 

 planation of how the worm maintains its direction toward the 

 source of stimulation after withdrawing into the sand is not 

 clear. It appears likely, however, that this directive response is 

 a movement toward areas where the chemical substances given 

 off by the food, and infiltrated through the sand, show higher 

 concentration. The sense of sight plays an insignificant if any 

 part in these reactions, for if a pipette ful of filtered clam extract 

 is substituted for the clam in an experiment like that just de- 

 scribed, the worms show the same responses, extending their 

 bodies toward the center of the dish where the extract was placed. 



In the laboratory as well as in natural surroundings we never 

 saw the animals lose contact with their burrows during their 

 movements over the sand in response to food excitation. They 

 were tested by moonlight in the laboratory with food but no 

 difference from behavior in daylight was noted. 



For some time after the first observations on Nereis were 

 made we were unable to explain how the stimulating material 

 derived from the small quantity of food used in some of our 

 experiments penetrated the burrows in sufficient amounts, and 

 quickly enough, to call forth such prompt reactions. The solu- 

 tion of this problem was found when worms were allowed to 

 enter glass tubes, open at both ends, the calibers of which were 

 nearly the same as those of their burrows. Tubes of this sort are 

 soon lined with mucus and the worms remain in them for hours 

 at a time, exactly as they do in the sand. No difficulty was ex- 

 perienced in inducing them to enter the tubes. It was only 

 necessary to direct the head into the opening, after which the 

 worm moved forward of its own accord ; and once well inside 

 stopped locomotion. In the tube Nereis exhibits a most striking 



