Hadley, Behavior of the American Lobster. 275 



there usually resulted a forward rotation through 180°. This 

 reaction caused the larva to become oriented (often on the 

 bottom) with the back below and the head toward the previously 

 existing source of light. This position was not maintained, but 

 was su^cceeded by a "righting reaction," usually a revolution on 

 the longitudinal axis, which brought the back again uppermost. 

 After this response the larva might swim in diverse directions. 



Case II. Larva oriented with the back above and the head aivay 

 from the li^ht, which comes slightly from the stde—U, when the 

 larva was oriented as described above, the light was suddenly 

 cut off, there resulted a swing of the long body-axis so that the 

 larva was brought more or less nearly to face in the opposite direc- 

 tion; i. e., in the direction from which the light had previously 

 come. This orientation, however, was not permanent, but other 

 consequent reactions occurred and the larva might swim in one 

 of several directions. 



Case 12. Larva oriented as in Fig. 17, J5'— If the direction ot 

 the light was from above, and the orientation of the larv3e as in 

 Fig. 17,5', when the light was cut off, the head of the larvae would 

 swing upward to face the direction from which the rays had pre- 

 viously come. Consequently, however, the orientation became 

 that of the normal swimming position. 



Case 13. Larva oriented as in Fig.20,B'—V^hen, as the result 

 of Hght stimulation from below (as in Case 9), the larva was oriented 

 witlf the head directed upward, and the illumination was sud- 

 denly cut off, the head of the larva would swing downward to face 

 the direction from which the light had previously come; sometimes 

 the larva would perform a rotation in an arc of greater or less extent 

 and fall to the bottom. The body-orientation with head down- 

 ward was not maintained, however, but was at once superseded 

 by the normal swimming position. 



It thus appears from these cases that there was usually an excess- 

 ive movement to produce the new body-orientation; but that 

 these movements invariably ended in the assumption of the nor- 

 mal swimming position. 77; 

 Resume of experiments on the effects of direct lighting and shad- 

 ing— (A) The effect of suddenly submitting the larval lobsters 

 to a light which has a directive influence is to cause the larvae to 

 orient themselves in such a manner that the longitudinal axis ot 

 the body finally assumes a definite relation to the direction ot the 



