THE AMERICAN LOBSTER. 
189 
cunuers 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 larvae, 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. m. the surface on the lee side of the pool swarmed with larvae. 
Occasionally one could 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 tish 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 larvie immediately 
gathered on the side of the dish nearest the window. Turn the dish slowly through 
an angle of 180 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, ligli could enter only from above. 
When larvie were placed in this, the stronger always rose toward the source of light 
into the ill umiuated 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 larvie swam up to the surface in different parts of the jar. When the diffused or 
direct sunlight was admitted only at the end the lame 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 larvie 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 larvie 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 Ryder found that under similar 
circumstances the larvae gathered on the side nearest the source of light 2 (172). 
The general conclusion reached, that larvie 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 larvie which 
I have already given. The taking of larvie 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. 
2 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.” 
