Hadley, Behavior of the American Lobster. 287 



head came to face, more or less obliquely, the dark background, 

 B' . The directive influence of the rays, however, continued to 

 draw the larvae on, but since they must travel in the direction in 

 which the tail pointed, they entered the arm b, and passing close 

 to the inside continued until further progress was prevented by 

 the end of the arm. Space will not be taken to show the numerical 

 results of this and similar experiments. Suffice it to state that 

 nearly all of the positively reacting larvae, of whatever stage or 

 age, when submitted to these conditions of experiment, reacted as 

 has been described above. This experiment was modified by 

 placing the Y-tube so that the uncovered arm of the tube rested 

 upon a piece of black paper. The results were invariably the 

 same; the majority of the larvae progressed to the arm of the tube 

 not overlying the black ground. 



Case 50 — In this case the conditions of the experiments were 

 further modified by reversing the Y-tube so that the arms pointed 

 away from the window. In this instance larvae which were mani- 

 festing a negative reaction were employed, and were first placed 

 in the end {a), nearer the window. When the light was admitted 

 the larvae at once oriented with their heads directed away from 

 the light and began to move away from the window. When they 

 had reached the point designated x, they immediately underwent 

 a swing of the longitudinal axis, as in previous cases, so that the 

 head was directed toward the black ground, bounding the outer 

 surface of the arm c. Thus they would continue, passing close 

 to the inner wall of the tube until the majority had gathered in 

 this arm. In this instance, however, the larvae would usually 

 rest between x and c, instead of moving to the end of the arm. 



Case ji — Here the black background bounding the outer side 

 of one arm was exchanged for a white ground of the same size and 

 having the position shown in Fig. 21 C. Third-stage larvae giv- 

 ing a positive reaction were employed for the experiment. They 

 were started in the end a. When the light was admitted, the usual 

 body-orientation resulted, and the larvae began their progression 

 through the tube toward the window. When they had arrived 

 at X they came under the influence of the white ground and turned 

 their heads away from this side. Progressive orientation then con- 

 tinued and the larvae eventually became grouped in arm c. Sim- 

 ilar results were obtained when half of this arm of the tube was 

 laid over a sheet of white paper. 



