Hadley, Behavior of the American Lobster. 223 



This resulted in a sudden and universal positive reaction which, 

 however, soon became indefinite. The larvae gradually returned 

 to the darker side of the jar and, as in the case mentioned above, 

 remained there so long as observed. 



Case /J. — When, on the other hand, another group of larvae which 

 was reacting positively to a light of low intensity, was brought by 

 slow degrees into a light of great intensity, there resulted no sud- 

 den, temporary change of reaction such as that observed above. 

 The reaction usually remained unmodified, but if it was reversed it 

 remained permanently so. The same statement holds for larvae 

 which had been reacting negatively to light of low intensity. When 

 they were brought by slow degrees into light of great intensity, 

 seldom did a sudden temporary change in reaction result. 



Conclusions from Experiment 14: The stimulation brought 

 about by suddenly submitting larvae to intense light may cause at 

 least two kinds of response: first, in the case of early first-stage 

 lobsters (about thirty hours old, and manifesting previously a posi- 

 tive reaction), a definite and universal, though temporary, negative 

 response; second, in the case of early second-stage larvae (about 

 five days old, and giving previously a negative reaction), a definite 

 and universal, though temporary, positive response. From Case 

 4 it appears that a gradual change of intensity (extending over an 

 equal or even a greater range of intensities) may not bring about 

 a similar result, although a permanent reversion in the reaction 

 may sometimes ensue. 



Larvae which have recently moulted are most susceptible to 

 slight differences in light-intensity; and the reaction of such larvae 

 is frequently negative, while the reaction of larvae which are 

 approaching the moulting-period is more often indefinite or 

 positive. 



Expernnent 75. Case I — The following experiment involved 

 the use of the Y-tubes described on p. 207. Ten positively 

 reacting lobsters, five hours old, were placed in the tube at the 

 end designated a (Fig. 5, B). The Y-tube was then placed in 

 position in the dark. Over one arm was laid a red glass, over the 

 other arm an orange glass, and then the screen was drawn from 

 the window to allow the light rays to strike the tube in the direction 

 shown in Fig. B. Tests were made about five minutes apart. 

 After each, the return of the lobsters to the {a) end of the tube was 

 induced merely by reversing the tube so that the end (a) was 



