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PROCEEDINGS OF THE AMERICAN ACADEMY. 



table shows, at all times, exhibited nearly the same percentage nega- 

 tive geotaxis. At the last trial made, it responded irregularly, and so 

 slowly, — at one time not changing its position for thirty minutes, — 

 that I had to give up the attempt to obtain a series. This was often 

 the case with other individuals after a few definite responses. 



Tests were then made on the geotaxis of the same individuals at 

 different times of the same day. Considering the slug's normal en- 

 vironment, it would not be surprising if, for instance, it should show an 

 upward tendency in the evening and a downward geotaxis in the day- 

 time. Its nocturnal habits and dislike of daylight might give it a dif- 

 ferent geotactic instinct at night from that of the daytime. I insert here 

 a table (in.) giving the results of a few experiments bearing on this 

 point. As the table shows, the response is pretty constant at different 



TABLE in. 

 Geotaxis of three Individuals at Different Times in the Day. 



times of the same day. The one exception is number 2. That it 

 was negative on one evening at 7 p. m., may be explained by the fact 

 that its condition was not good. Moreover, on another evening at the 

 same time the animal had become positively geotactic. 



From the observations recorded in Tables III. and IV., it is plain that 

 the geotactic response is not due to purely accidental factors, but can 



