FRANDSEN. — REACTIONS OF LIMAX MAXIMUS. 201 



uals. The geotaxis of each animal was tested on three different sur- 

 faces, — the glass plate, a circular wooden plate, and a glass plate coated 

 with vaseline. Care was taken to have other conditions as nearly as possi- 

 ble the same. Circular plates were employed so that the animal could be 

 rotated into a horizontal position without beiug touched by the hand. In 

 several cases a series was made on an animal using the glass surface ; 

 the animal was then transferred to a wooden plate and the same number 

 of trials made ; the same individual was then put back on the glass plate 

 and as many more tests were made ; finally, it was returned to the wooden 

 plate and an equal number of observations made. The same thing was 

 tried alternating between glass and vaselined surfaces. 



The second column shows what per cent of the length of the posterior 

 region of the animal's body its anterior region is, as previously defined. 

 A comparison of the columns " % Geotaxis " under the different con- 

 ditions at 'once shows, in nearly every case, a marked difference in the 

 geotactic response with the three kinds of surfaces. The same number 

 of trials was not always made on a given animal under the different con- 

 ditions, so that the comparisons are not always on exactly the same basis. 

 The results, however, prove pretty conclusively that all animals have an 

 inherent tendency to move- toward the earth. On the glass plate, the 

 animals moving upward and downward are about equal in number, the 

 rea-^ons for which we have already given. On the wooden plate, which 

 affords the best of the three surfaces for adhesion, all the animals have 

 become positive. A vaselined surface offers still greater difficulties to 

 positively geotactic responses ; it compels the positively geotactic animals 

 to become negative (Nos. 2,5, 8, 10). Some animals are utterly unable 

 to adjust themselves to this extraordinary condition, especially if not en- 

 dowed with the power of secreting excellent mucus. These animals either 

 vainly cling with the anterior end of the body to the plate, while the poste- 

 rior region slips downward, thus directing the animal up, or they roll off the 

 plate altogether as soon as it is placed in an inclined position. For this 

 reason some of the animals negatively geotactic on the glass plate gave 

 no geotactic response when they were placed on the vaselined surface. 

 These facts, then, conclusively answer in the affirmative our second ques- 

 tion. All slugs have a tendency to move toward the earth. 



Now the question naturally comes up, Can we not assist this tendency 

 in those animals which are negatively geotactic on a glass surface by 

 bringing some other stimulus — light, for example — to bear upon them ? 

 This slug is negatively phototactic to strong light, as the third part of 

 this investigation will show. By exposing the animals to sti'ong light, can 



