240 REPORT OF COMMISSIONERS OF INLAND FISHERIES. 



The method of conducting a single experiment was essentially as 

 follows: The box was filled with salt water to a depth of two inches, 

 or thereabouts, and placed in a quiet and level position. The de- 

 sired number of lobsters, together with sufficient salt water to make 

 the total depth about three inches were added. When the water had 

 quieted and the young lobsters had arranged themselves more or 

 less uniformly in the water area, the cover was placed in position. At 

 intervals, varying from five to fifteen minutes, the cover was removed 

 and the position of the young lobsters was observed. After some of 

 the observations the cover would be reversed in position, so that the 

 illuminated area in the water would be changed to the opposite end 

 of the box. After other observations, however, the cover would be 

 left as in the first instance, or removed entirely until another uni- 

 form distribution of the young lobsters had been obtained. Whether 

 the position of the cover was changed or not, the results, with few 

 exceptions, agreed with great uniformity. 



The light intensity was regulated by the time of day at which the 

 observations were made, either at noon, mid-afternoon or nearly 

 evening. In this way, without using artificial means, it was possible 

 to regulate the degree of light intensity with a very fair precision. In 

 the case of studying monochromatic lights (red and blue) sheets of 

 glass were used, the plate being placed over the entrance of the tube. 

 Without doubt, liquid filters would have been an advantage; but the 

 experiments which were made with glass plates gave such definite 

 reactions that they were judged satisfactory for preliminary work. 



The counts were made by dividing the field into three areas, 

 namely, the illuminated, the mid-area, and the dark. Owing to the 

 fact, however, that the illumination in the mid-area must have been 

 almost imperceptible, for practical results it might have been quite 

 safe to include the mid-area counts with those of the dark area, but 

 for sake of definiteness they have been considered as a separate area. 

 In the greater number of cases it was an easy matter to count the 

 number of individuals in each of the three areas before a change in 

 position took place. Twenty individuals were, in most cases, used 



