Hadley, Behavior of the American Lobster. 



273 



directions of the light (as both from the side and from above) 

 produced modification in the reaction, but these could at any time 

 be predicted if the individual constituents of the light were known. 

 Case g. Larva oriented zvith back belozu; light enters from belozu 

 — Under the conditions of orientation stated above the resulting 

 reaction was similar to that described under Cases 6 and 8, but 

 reversed. As in these instances, one of two results usually oc- 

 curred: (i) The larva would undergo a forward rotation 

 through a variable number of degrees, and assume directly a new 

 "swimming-position" as shown in Fig. 20, B'. It was readily 

 observed that the head was directed upward and away from the 



Fig. 20. For description, see Case 9. 



light, not downward at an angle of about 30° from the hori- 

 zontal, as in the normal swimming position; (2) it might happen, 

 however, that instead of assuming this orientation the larva would 

 merely come to an orientation with the back below and with the 

 head directed upward as a slight angle as shown in Fig. 20, C'. 

 It might, again, undergo one or more complete rotations forward, 

 through 360° and then assume the new position shown in Fig. 

 20, B', which position might be retained as long as the light 

 conditions remained unchanged. The definiteness in these two 

 reactions could be modified, as a result of changing slightly the 

 direction of the light. 



