THE CHEMICAL SENSE OF NEREIS VIRENS. 



233 



physical factor, influenced the animal's response. To such 

 stimuli no response occurred, although the worms appeared 

 promptly when crab's meat was placed in the same situations. 

 The evidence, therefore, supports the view that a chemical sense 

 is the primary one upon which its responses to animal food 

 depend. 



Certain striking features of recorded behavior may now be 

 considered. It was early noted that when a worm appeared 

 from beneath the sand in response to chemical stimulation there 

 was little uncertainty shown in the direction of its movements. 

 Almost invariably it advanced toward the bait which, if not too 

 far away, was generally found without difficulty. It was also 

 observed that, when the food was out of reach., the worm with- 

 drew into its burrow only to reappear, frequently in a position 

 nearer the source of the stimulating material. In order to study 

 these directive reactions further a number of animals were col- 

 lected and brought into the laboratory. They were kept for a 

 time in dishes containing water and sea lettuce, and under these 

 conditions they would often take from forceps small pieces of 

 meat offered them. In fact, all of the foods to which the worms 

 reacted in their natural habitat were also accepted as they moved 

 about in the folds of sea lettuce, enclosed more or less by mucous 

 secretions. Under these conditions, however, they were easil) 

 disturbed and their somewhat erratic feeding behavior indicated 

 that they were unfavorably situated for any detailed experi- 

 mental study of their chemical reactions. Accordingly four 

 worms were placed in a circular glass dish having an inside 

 diameter of 28 cm. and containing sea water and sand. The 

 layer of sand was approximately 2.5 cm. deep. The animals 

 immediately entered the sand, forming burrows lined with mucus 

 which here and there connected with the surface by well marked 

 openings. They showed no tendency to leave the burrows if 

 the dish remained undisturbed. After preliminary tests, which 

 demonstrated that the worms would react to food juices as 

 readily as they did in their natural surroundings, three similar 

 experiments were performed, one of which is described in some 

 detail in the following paragraphs. 



