Hadley, Behavior of the American Lobster. 235 



In consideration of the apparent fluctuations in the sign of reac- 

 tion manifested by the above-mentioned larvse, it may be noted 

 that these lobsters represented a group in which some were 

 **early," others " advanced, " third-stage larvae. Indeed many were 

 approaching the third moulting-period; the significance of this for 

 the behavior of the larvae we shall consider in the next few cases. 



Case 5 — July 27, 2 p.m. Thirty eleventh-day, third-stage lar- 

 vae were transferred to the glass jar and placed in the dark box. 

 Under colored lights, although the general reaction was negative, 

 many were positive. Experiments made upon the larvae in the 

 glass-bottomed box B to determine the photopathic reaction at this 

 time, showed that the larvae gave neither a definitely positive nor 

 a definitely negative reaction. Other tests indicated a definitely 

 positive reaction. When, however, light was admitted to the box 

 through the end window (as well as through the bottom), first 

 from the red end, then from the blue end, of the box, there resulted 

 a definite negative phototactic response. The arrows show the 

 direction in which the light entered the box. 



— > Red. Blue. Orange. Green, 



I 2 I 6 



I I 09 



o o o 10 



— > Red. Orange. Green. Blue. 



o o o 10 



0019 



Red. Orange. Green. Blue. < — 



5122 

 6022 



The foregoing cases demonstrate that these larvae manifested 

 a definitely negative phototactic reaction under the conditions of 

 illumination described; and that, by those rays which had a direc- 

 tive influence, they could be driven into a region of either greater 

 or lesser light intensity, as represented by the blue and by the red 

 ends of the box, respectively. It might be argued that, so long as 

 the eyes of the larvae are homolaterally stimulated, variations in 

 intensity can not cause or change the orientation, and that orienta- 

 tion results only from a heterolateral stimulation. But this is by 

 no means true, for it has been noted in the foregoing pages, and 

 it will be further demonstrated, that slight differences in intensity, 



