Hadley, Behavior of the American Lobster. 225 



the other. These glasses were used in the next experiment. The 

 darker of them may be designated as red, the hghter as ruby. 

 The resuks of four tests were as follows : Ruby arm, 21 ; stem, 10; 

 red arm, 9. In the last experiment, with this group of larvae, it 

 was found that a great intensity of light, striking the red slides, 

 was required to bring about reaction; and that, even then, several 

 larvae would remain in the region designated x (Fig. 5, B), near 

 the junction of light and dark. These experiments were repeated 

 with both black and white backgrounds for the arms of the Y-tube. 

 The results agreed with great uniformity, differing only in the 

 length of time required for the reaction. From these last experi- 

 ments we may conclude that the first-stage lobsters, at the age of 

 five hours or less, are extremely sensitive to slight diflPerences in the 

 intensity of light, more so in fact than older lobsters of the first 

 and later stages; for it was seldom with these older lobsters that 

 the delicate reaction to the ruby and the red glasses observed m 

 Experiment 15, Case 3, could be induced. 



Expermient 16. Twenty first-stage larvae, slightly over two 

 days old (for which to light of nearly all intensities reactions on 

 the first and second day had been positive), were put in the glass 

 jar, and this in turn was placed in the dark box. They were sub- 

 mitted to light from a small window one inch wide and two inches 

 high, before which the colored glass plates could be placed so as 

 to illuminate one side of the jar with red, blue, green, or orange 

 rays, as the case might be. The reaction in each of these lights 

 was as follows: 



Ljpjj^_ Positive. Negative. 



Red 2° ° 



Orange ^o ° 



Green '9 ^ 



Blue i8 2 



White* 15 5 



Day 3 17 



* Subdued daylight passing through one or two thicknesses of white paper. 



Here it is shown that the negative reaction to lights of great 

 intensity, which was first discovered in larvae thirty hours old (Ex- 

 periment 14, Case i), and which, as we shall see, persists^ for a 

 variable length of time, has become accentuated and remains for the 

 time permanent. The next series of observations were made upon 

 lobster larvse on the fourth day after hatching. Many of them 



