676 



SCIENCE. 



[N. S. Vol. XXII. No. 569. 



The method of conducting a single experi- 

 ment was essentially as follows : The box was 

 filled with salt water to a depth of 2 inches 

 or thereabouts, and placed in a quiet and level 

 position. The desired number of lobsters, to- 

 gether with sufficient salt water to make the 

 total depth about 3 inches were added. When 

 the water had quieted and the young lobsters 

 had arranged themselves more or less uni- 

 formly in the water area, the cover was placed 

 in position. At intervals, varying from 5 

 to 16 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 observa- 

 tions, however, the cover would be left as in 

 the first instance, or removed entirely until 

 another uniform distribution in the position 

 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 degree of 

 precision. In the case of studying mono- 

 chromatic 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 marked and 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 surety 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. The number of twenty 

 individuals was, in most cases, used for ex- 

 perimentation, for so small a number distrib- 

 uted over three areas could be taken in at a 

 glance, and furthermore twenty seemed a suffi- 

 cient number to give representative results. 

 In the following account are recorded experi- 

 ments carried on with the first five stages < 

 Homarus. All the conditions of light and 

 backgrounds were not brought to bear upon 

 all five stages, and only a sufficient number 

 of experimentation reports are here recorded 

 to show the general drift of the results. 



EXPERIMENT I. 



Conditions: black hachground; sunlight dull; 



20 first stage larvae. 

 Test. Lt. End. Mid-area. Dk. End. Cover. 



1 2 6 12 



2 ,3 4 13 Reversed. 



3 1 5 M 



4 3 4 13 Reversed. 



Similar results were obtained when a greater 

 intensity of light was used. 



EXPERIMENT II. 



Conditions: white hachground; sunlight dull; 



20 individuals used, first stage. 



Test. Lt. End. Mid-area. Dk. End. Cover. 



1 2 5 13 



2 2 2 16 Reversed. 



3 2 3 15 Reversed. 



4 1 5 14 



EXPERIMENT III. 



Conditions: white hachground; sunlight hright; 



30 individuals used, first stage. 

 Test. Lt. End. Mid-area. Dk. End. Cover. 



1 22 4 4 



2 18 7 5 ^Reversed. 



3 20 7 3 



These results seem to show that the first 

 larval stage of Homarus is negatively photo- 

 tropic on a black background, with both dull 

 and bright light; but that while on white 

 backgrounds he is, under low intensity, nega- 

 tively phototropic, if the intensity of light 

 becomes greater he becomes positively photo- 

 tropic. Similar results were obtained with 



