212 "Journal of Comparative Neurology and Psychology. 



the red extremity of the box was opened to the diffuse Hght of the 

 room. The result was that the larvae immediately oriented to 

 the new rays, left the region of greatest light-intensity, the blue 

 area, and moved backward in the direction of the incident light 

 rays toward the source of the weaker light and, at the same time, 

 into a region of lesser light-intensity at the red end of the box.^ 

 The distribution at the end of 19 minutes was as follows: blue, 

 4 individuals; green, i; orange, i; red, 24. Here it appears that 

 the larvae, which at the beginning of the experiment were grouped 

 in the area of greatest illumination under the influence of non- 

 directive rays, were forced by the directive influence of the new 

 rays to move from a region of greater into one of diminished 

 light-intensity. As will be observed later, this experiment was 

 tried under a great variety of conditions, and with larvae of difi^er- 

 ent stages and ages, with uniform results. Whenever the larvae 

 had an opportunity to move in the direction of the rays, they would 

 do so, notwithstanding the fact that they thus passed from a region 

 of greater to one of less illumination. 



In the paragraphs immediately preceding, the purpose has 

 been merely to indicate that in the behavior of the lobster larvae 

 we may observe reactions both to the intensity of light and to the 

 directive influence of the light rays. The latter depends, first, 

 upon the unequal stimulation of the two eyes, and second, upon 

 the degree of illumination which affects both eyes. The con- 

 clusions which have been drawn from these few experiments 

 receive further support from other experiments. But first, it is 

 necessary to know whether there is any form of reaction common 

 to all larval lobsters. To answer this question, which is of pri-' 

 mary importance, it will be necessary to report in detail a series 

 of tests, which were made upon many groups of lobsters during 

 different periods of their metamorphosis and under difi^erent con- 

 ditions of stimulation by light. 



Experi7nent yf.. Case I — In several instances larvae which had 

 been hatched from One-half hour to one hour were put in a glass 

 jar, which was in turn placed in the dark box and submitted to 

 illumination on one side from a narrow window. In every case 



^ If this experiment appears uncritical because of the lack of information regarding the exact inten 

 sities of light at the opposite ends of the box, it may be answered that the intensity of light was measured 

 by the only method available. Sensitized paper was placed inside the box, one strip over the end win- 

 dow, the other over the bottom at the blue end. The results showed that the light entering the blue end 

 through the bottom of the box was much stronger than that entering the end window from the room. 



