Hadley, Behavior of the American Lobster. 265 



ing the amount and the general direction of the hght which they 

 reflected or absorbed. First, however, we shall consider the effects 

 of suddenly throwing the light from a certain direction upon larvae 

 oriented in various positions. 



Case I. Illumination from before — In the first instance the 

 behavior of a single larva was studied (the stage does not matter). 

 It was oriented in the rectangular container, in the dark box with 

 its head toward the three by one inch window, which was closed 

 (Fig. 10), but in such relation to the glass box that its longitudinal 

 axis was parallel to the direction of the rays of light coming from 

 this window^ when it was opened. While the larva was so oriented, 

 the screen was drawn aside and light from the small window was 

 allowed to strike the larva "head-on. " Under these conditions, one 

 of two reactions resulted. The larva underwent either a forward 

 or a backward somersault, or rotation, which brought the back 

 below with the head directed away from the source of illumination. 

 Whether the rotation was backward or forward made no differ- 

 ence in the resulting orientation and which one occurred depended 

 upon the direction of the rays of light which struck the eyes of the 

 larva. In normal swimming the body of the larva in any of the 

 first three stages is bent about 30° from the horizontal. Now 

 if the rays of light had the direction of A or B (Fig. 12) the 

 rotation was usually forward, while if the light came from below, 

 direction C, the rotation often was backward. After this first 

 orientation the larva (position B') frequently performed a rotation 

 on its long axis, either to the left or right, which brought the back 

 again uppermost, and it then progressed in the direction of the 

 rays, either toward or away from the source of illumination. 



Corollary i — If the rays striking the eyes of the larva had the 

 slightly oblique direction shown in Fig. 13, a or c, but were in direc- 

 tion or plane B (Fig. 12), then the larva pivoted at the middle of its 

 own longitudinal axis and swung to one side or the other, always 

 keeping the back uppermost. 



If the rays of light took the direction designated a^ — a* or 

 c^ — c\ the result was the same; the larva swung until the longi- 

 tudinal body-axis was parallel with the incident rays, and the head 

 was directed away from the source of illumination. 



Corollary 2 — If the rays striking the eyes of the larva had the 

 oblique direction, a^ — a'^ or c^ — c^ (Fig. 13) in plane A of Fig. 12, 

 then the resulting movement was a combination of the forward 



