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PROCEEDINGS OF THE AMERICAN ACADEMY. 



After being on the vaselined surface, there was a noticeable decrease in 

 the power to hold on to the glass or wood, due probably to the vaseline 

 which still adhered to the animal. Regarding these cases as typical of all 

 slugs, we can say that the wooden surface affords a condition nearly 

 twice as favorable as that of the glass plate for the exhibition of an inter- 

 nal tendency. The vaselined surface, on the contrary, is only about half 

 as fixvorable as the glass plate ; that is, it doubles the obstacles. As a 

 general rule, owing to the irregularities of other iniiuences, the differ- 

 ence between the different surfaces would be, probably, somewhat less. 

 For active, well-conditioned animals, however, we have no hesitation 

 in concluding that the ratios obtained from these cases are fairly 

 rejjresentative. 



Having thus established the fact that the character of the surface does 

 modify the animal's power to attach itself, I next give a table (VII.) 

 showing the results of a series of experiments on twelve different individ- 



TABLE VII. 

 Geotaxis of the Slug on Different Surfaces. 



