286 journal of Comparative Neurology and Psychology. 



whose arms are at the bottom, for larvae having a negative phtoto- 

 tactic reaction. In tubes A and B one side of one arm was fitted 

 with a band of black paper which extended half over the circum- 

 ference of the arm and a very short distance down each stem. 

 In tubes C and D the same arrangement existed, save that white 

 instead of black paper was used. In every case the light rays 

 came from the window in the direction of the arrows. In all 

 cases of larvae manifesting a negative reaction, the start was made 

 at the end of the tube (lying horizontally on the table) nearer 

 the window. In the case of positively reacting larvae, the start 

 was made from the end of the tube farthest from the window. 

 The end marked a in every instance was the end frorri tuhich the 

 larvae moved, the purpose of the test being to determine in which 

 arm of the tube the larvae would eventually gather. 



Fig. 21. Showing the Y-tubes set up for experiment. In every case the light came from above 

 in the direction of the arrows. The tubes whose arms are above were set up for positively reacting 

 lobsters; those whose stems are above, for negatively reacting lobsters. In tubes A and B the cross- 

 hatched areas represent the part covered with black paper. In tubes C and D the clear area was covered 

 with white paper. Tubes E and F are shown equipped with the glass plates placed over the arm. 

 In every instance the larvae were started from the end of the tube designated a. For further explanation, 

 see Cases 29-33 •'^'^v PP- 286-289. 



Case 2g — The tube was arranged as in Fig. 21, y^. Ten posi- 

 tively-reacting, first-stage larvae were placed in the Y-tube, and, 

 by certain manipulations of the light and by virtue of their positive 

 reaction, they were made to congregate in the stem end. Then 

 suddenly, the direction of the light was changed so as to come in 

 the direction of the arrows. Immediately the larvae oriented with 

 their heads toward the end a, and passed through the tube toward 

 the light. As soon as they approached the region marked x they 

 came under the influence of the dark background bounding the 

 side of the tube. Immediately, as we have seen to be the case in 

 previous instances, the longitudinal body-axis swung so that the 



