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PROCEEDINGS OF THE AMERICAN ACADEMY. 



ary until the worm had crawled to the outer circle marked on the table, 

 a distance of 15 cm. When it was desired to test the worm headed in 

 the opposite direction, it was only necessary to shift the screens d and 

 (V to the other side of the directive axis. This arrangement proved 

 to be much more satisfactory than the one first employed, the results 

 being free from the disturbing factor of thigmotaxis. 



Figure 5. Record of five successive trials with an earthworm exposed to the 

 influence of the large area of illumination and headed away from the observer. 

 For fuller explanation see text. 



The difference in the results in these two cases emphasizes the im- 

 portance, in work of this nature, of bearing in mind and eliminating, as 

 far as possible, all extraneous influences. 



Before describing these experiments and their results, it may be 

 well to describe in some detail the methods employed in keeping the 

 records, since the same description will apply in the case of most of 

 the animals studied. Figure 5 shows a record of five successive trials 

 with a single worm, — in this case exposed to the influence of only 

 one light (the one having the larger area), which was situated at the 



