GEOTROPISM OF THE MARINE SNAIL, LITTORINA LITTOREA. 59 



possibly to fatigue. The same individuals could be used only 

 for four or five trials. Ten individuals, sometimes II or 12 

 (with anticipation of falls), were used for each trial of a series 

 of experiments. As will be seen in the tables, however, very often 

 less than 10 individuals were left on the support for observation, 

 the rest having fallen down. 



2. Methods. Loeb's method (8) modified by Davenport and 

 Perkins (2) and by Frandsen (3), of the different angles of in- 

 clination of a support, on which the animals are to be placed, was 

 adopted with variations. The support was a plain glass plate 

 about 22 x 19 cm., marked off on one side into squares of one 

 sq. cm. each, whereby it could be readily determined how far the 

 animals moved from their original places. 



The support, or plate, was placed in an apparatus by which it 

 could be held at any ten-degree angle between the horizontal and 

 vertical (see Fig. i). 



FIG. i. G. P. = a plain glass plate. The rest of the apparatus is all wood. 



The animals were placed on the unlined side of the plate, 

 moistened and held upside down at an inclination, say 10 to 



