130 'Journal of Comparative Neurology and Psychology. 



On August 10, 1905, between 20 and 30 colonies were put into 

 the aquarium into an intensity of 21 candle meters. When the 

 rays were parallel with the bottom the group spread very little 

 and swam across the aquarium nearly parallel with the rays. But 

 when the glower was lowered so that the rays passed up through 

 the glass bottom of the aquarium, making an angle of 25 degrees 

 with it, the group spread out considerably and the majority deflec- 

 ted quite sharply to the right. The largest colonies were found 

 along the right side of the column and the smallest along the left, 

 under both conditions. It is doubtful whether the smaller colo- 

 nies changed their course after the position of the glower was 

 changed, but the larger ones certainly did. Later more definite 

 results were obtained by experimenting with a single colony. The 

 specimen selected was of medium size and contained quite a num- 

 ber of rather small daughter-colonies. When the rays were par- 

 allel with the bottom this colony deflected three degrees to the 

 right, but when the light was below the level of the bottom and 

 came up through it so that the rays made an angle of 25 degrees 

 with it, the organism deflected 19 degrees in the same direction. 



In ascertaining these deflections the colony was allowed to cross 

 the aquarium a few times first with the rays parallel with the 

 bottom, then with the rays at an angle of 25 degrees with it, then 

 again with the rays parallel with it, and finally, with the rays at an 

 angle of 25 degrees. The deflection during the various trips under 

 each condition, was nearly constant. It is therefore certain that 

 the increase in deflection was not due to a possible change in the 

 physiological condition of the organism. Neither was it due to 

 difference in light intensity, for the strength of illumination was 

 nearly the same under the two conditions of the experiment, and 

 deflection is not much affected unless there is very marked change 

 in the intensity of the light (see p. 122). 



In moving toward the light in rays parallel with the bottom, the 

 axis of this colony was at an angle of about 12 degrees with the 

 bottom. The organism moved near the bottom of the aquarium 

 so that the posterior end appeared to be slightly in contact with it. 

 But when the light came from beneath at an angle of 25 degrees the 

 axis of the colony was nearly horizontal and the organism moved 

 so near the bottom that the cilia must have come in close con- 

 tact with it. As the specimen thus swam across the aquarium the 

 axis could be clearly seen to swing at short intervals, from a posi- 



