PEARL AND DE WITT ON REACTIONS OF SLUG AGRIOLIMAX. 79 



CERTAIN REACTIONS OF TIIK COMMON SLUG AGRIOLIMAX 



CAMPESTRIS BiNNKY. 



BY RAYMOND PEARL AND MAUD M. DK WITT. 



(Abstract.) 



1. Tlie reaction most studied was that given by the sl-ug on encoun- 

 tering the edge of the solid body on which it was crawling. 



2. The usual reaction of the animal on coming to the edge is to 

 pass over and hang for a time by the mucus thread secreted by the 

 foot. 



3. Approximately two-thirds of all the slugs tested react in this way 

 on coming to the edge for the first time. 



4. It is found that this positive reaction changes to a negative after 

 the animals have encountered the edge a certain number of times. That 

 is, the slug does not crawl off after a number of trials. 



5. This change in the reaction does not seem to be due to general 

 weakness, or to the diminution in the supply of mucus, or to any process 

 of ''learning'' on the part of the slug; but is, apparently, merely an ex- 

 pression of a sort of "physiological variability" of the organism. 



