4 LEON J. COLE 



as possible around an axis passing through the center of the 

 starfish and perpendicular to the surface upon which it was 

 crawling. The presence of all external stimuli (mechanical, 

 chemical, thermal, and light) can no more be eliminated than 

 can those of internal origin, but so long as they are uniform 

 over the entire animal, or bear to it the radial relation mentioned 

 above, they need not be considered. 



The earlier experiments were performed in a large circular 

 glass dish, 36 cm. in diameter, 13 cm. deep, and having a flat 

 bottom. At the beginning of each period of experimentation 

 this dish was filled with fresh sea water to a depth of about 10 

 to 15 cm. It will be seen that at the central point on the bottom 

 of this dish the requirements stated above regarding mechani- 

 cal, chemical and thermal conditions must have been very well 

 met. Light could, of course, have been excluded entirely, ex- 

 cept for its desirability in enabling the experimenter to observe 

 the behavior of the subject. Accordingly the dish was illumi- 

 nated by the light from an incandescent electric bulb at the 

 ceiling some 6 or 7 feet above, and directly over the center of 

 -the dish. Extraneous light and unsymmetrical reflection were 

 prevented by means of a cylinder of black cloth, supported on 

 hoops, and pendant from the ceiling, with the lamp at its center 

 above, and enclosing the glass dish below. As a further pre- 

 caution, the experiments were all performed at night, when out- 

 side the cloth cylinder was darker than within. A small peep 

 hole permitted observation of the interior, while, by passing 

 the hand beneath the cloth, the specimen could be manipulated. 



At New Haven the experimental conditions were essentially 

 the same, except that a glass dish of sufficient size not being 

 available, a small pressed paper wash tub was used in its place, 

 and the experiments being conducted in a dark-room, the cloth 

 cylinder was dispensed with. 



In the experiments made for determining simply the direc- 

 tion of locomotion, ten starfishes (designated Nos. 1 to 10) were 

 used, with each of which fifty trials were recorded. Owing to 

 the limitations in size of the receptacles employed, compara- 



