THE AMERICAN LOBSTEK. 189 



cunners then made their appearance and snapped up the larvae right and left. Two 

 hours later the lobsters were diffused over the whole surface of the pool, a large num- 

 ber of them swimming close to the surface. The paler larva?, with chromatophores 

 contracted, can not be easily distinguished at a distance of a few feet, but when one 

 of their eyes is turned at the right angle it glows, like a minute electric spark, with a 

 greenish light. At 1 p. in. the surface on the lee side of the pool swarmed with larva'. 

 Occasionally one cotxld be seen to attack and drag another down. They swim about 

 aimlessly with considerable rapidity, now rising or falling, and changing their direction 

 frequently. The majority had now become quite red. Later in the afternoon nearly 

 all had disappeared, having been swept out by the tide or destroyed by the dinners 

 and other lish in the pool. 



Experiment 2. — On July 13, 1894, 1 placed a number of larvae, mostly in the first 

 stage, in a glass dish, next to the window in the hatchery. The larva? immediately 

 gathered on the side of the dish nearest the window. Turn the dish slowly through 

 an angle of ISO degrees, and the lobsters invariably flock toward the source of light. 

 This may be repeated indefinitely, but always with the same result. 



Experiment 3. — A box was made with blackened sides, so that when a glass jar 

 was set in it vertically, with its upper end exposed, ligh could enter only from above. 

 When larva? were placed in this, the stronger always rose toward the source of light 

 into the illuminated zone. Some, however, apparently the weaker ones, remained below. 



Experiment 4. — A light-proof box was then constructed with sliding lid and end, 

 so that a long, closed jar could be laid in it horizontally. When the lid was removed, 

 the larva? swam up to the surface in different parts of the jar. When the diffused or 

 direct sunlight was admitted only at the end the larva? invariably flocked toward the 

 illuminated end and remained there. If any lagged behind, it was because they were 

 too weak to swim. 



These simple experiments 1 seem to show conclusively that under ordinary circum- 

 stances the larva? of the lobster are positively heliotropic. I made no experiments on 

 the effects of changing the temperature conditions. The temperature of the water 

 used was the same as that of the water running through the aquaria, or about 1° 

 higher than the water temperature of the harbor (see table 2). 



The second experiment was tried in the summer of 1893 with the reverse result, 

 the lobsters swimming away from the source of light, showing possibly that under 

 certain conditions the larva? are negatively heliotropic (97, p. 82). This experiment is, 

 however, the least trustworthy of all, since there are al ways cross lights in a room and 

 the conditions are consequently changing. Professor Eyder found that under similar 

 circumstances the larva? gathered on the side nearest the source of light 2 (172). 



The general conclusion reached, that larva? swim up to the surface during the day- 

 time and stay there, probably sinking at night and rising again with the approach of 

 light on the following day, is supported by the record of the capture of larva? which 

 I have already given. The taking of larva? at night seems to be the exception; their 

 capture by day the rule. 



■In the course of these experiments I had the advantage of consulting with Professor Loeb,to 

 whose researches our knowledge of heliotropism in animals is very largely due. 



- He also says : "At night, or if light is shut off, the young lobsters go to the bottom of the tanks ; 

 and it seems they may then be most actively engaged in feeding if food is placed within their reach." 



