Hadley, Behavior of the American Lobster. 271 



with the longitudinal axis of the body bent at a greater angle from 

 the horizontal plane (Fig. 17, B'). This new swimming position 

 was usually maintained so long as the conditions of light remained 

 the same, but was sometimes replaced by the second form of 

 reaction, which usually occurred when the light had the direction 

 a, and which was merely an exaggerated form of the first. 



(2) In this second type of reaction the rotation of the larvae 

 was not limited to an arc of a few degrees, but was extended into 

 a forward "somersault." This in turn took place in one of two 

 ways: {a) the larva might accomplish a rotation of 360° and 

 return to its original position with the back above, but since the 

 stimulation from above remained the same, it would not rest in 

 this position, but would continue for a time to perform complete 

 rotations without pause, after which it would come to rest as shown 

 in Fig. 17, B' . This new swimming position was sometimes 

 maintained as long as the conditions of light remained unchanged, 

 though it might give place to further rotations; {b) the larva might, 

 as a result of the forward rotation, come to rest with the back 

 directed below, but this orientation was only momentary, because 

 the influence of the light from above immediately determined a 

 backward rotation. This last reaction might culminate when the 

 larva had gained the new position shown in Fig. 9, B', or it might 

 be continued into one or more backward rotations through 360° 

 and culminate after a greater or less number of such rotations, 

 by coming into the new swimming position mentioned above. 

 This orientation would be maintained as long as the same condi- 

 tions of light were in effect; or it might be interrupted from time 

 to time by rotations in arcs of varying degrees, and in either of 

 the directions mentioned above. 



Corollary i — If, when the larva was oriented as in Case 6, the 

 light was introduced from both sides and above, the resulting reac- 

 tion was a combination of the forward rotation and the side swing. 

 If the light came from above and behind (Fig. 17, ^,then the direct 

 assumption of the new swimming position B^ more frequently 

 resulted without the variable number of rotations through 180° 

 or 360°. 



Case 7. Larva oriented -with back beloiu; light enters from above 

 — Under the above conditions of orientation (Fig. 18) there was 

 usually one constant form of reaction. The larva would undergo 

 a backward rotation through about 120°, and come into a new 



