15^17] Mead: Notes on Emerita Analoga 435 



as shown by the more circuitous routes from the center to the peri- 

 phery. In an effort to confuse the animals still further in their sense 

 of direction, I gyrated some individuals more than two hundred revo- 

 lutions, after which they were quickly transferred to the plat used 

 in figure 2. The animals responded as in previous experiments hy 

 moving toward the ocean (fig. 3), although with perhaps less certainty 

 than in the case of the ungyrated specimens. 



To ascertain whether or not their direction was determined bj^ 

 sight, I repeated the experiment with specimens from which the eyes 

 had been removed. This time there seemed to be no tendency to move 

 in any one direction (fig. 4). I performed this experiment three times, 

 using a total of forty-five animals. In order to eliminate any .shock 

 that might ensue from the removal of the eye-stalks, I kept the blind 

 animals in an aquarium of running sea-water and performed the three 

 experiments at intervals of two and nineteen days respectively, with 

 similar results. 



As a consequence of the foregoing experiments and observations 

 it would seem that the eyes of these crabs play an important role in 

 guiding them to their feeding beds, should the.y by any means be 

 removed therefrom, and in apprising them of the proximity of birds 

 or other enemies. 



These animals are positively phototactic to low intensities of light. 

 When kept in the laboratory they congregate in greatest numbers at 

 the side of the aquarium nearest the source of light, unless there be 

 sand in the aquarium. 



Inasmuch as the animals were apparently controlled while in the 

 air by two infiuences, namely a down-hill tendency (geotaxis) and 

 an oceanward tendency, I endeavored to determine what intensity 

 of the former would exactly counteract the latter. In other words, 

 I wished to measure the intensity of the oceanward tropism in terms 

 of the tendency to move downhill, making i;se of the per cent of slope 

 as a unit of measure. After several trials I discovered that a slope 

 of one and three-fourths inches in twenty-five, or of 7 per cent, most 

 nearly satisfied this equilibrium. In confirmation I tried fifty animals 

 on this slope, with the result that they were fairly evenly distributed 

 in their direction tendencies. Figure 5 represents a t.ypical result 

 of an experiment of this series. Thus it seems that they cannot 

 "believe their own eyes" when confronted by a 7 per cent slope. 



It was my desire to make the burrowing instinct of the crabs the 

 basis of a series of labyrinth experiments, to test the habit-forming 



