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BULLETIN OF THE UNITED STATES FISH COMMISSION. 
that determines the depth-migrations of sea animals.” This has been abundantly 
demonstrated in Labidocera, where geotropism and chemotropism play parts as well | 
as phototropism, and probably much the same complexity obtains in many other 
organisms whose depth-migrations, though made simultaneously, may be really the 
results of quite different causes. 
CONCLUSIONS. 
1. Labidocera cestiva has a specific gravity in reference to pure water of 1.109, 
to sea water 1.082—. 
2. It falls through sea water at the average rate of about half a centimeter a 
second (a fathom in six minutes). It swims upward at about one-third this rate. 
3. In its fall it is oriented by the spread antennas, which keep the head upper- 
most. 
4. Its locomotor movements are either rapid uniform runs, or leaps, or rarely 
some intermediate form of movement. 
5. The runs are accomplished by the appendages between the anterior antennas 
and the tail. 
6. The leaps can be carried out by the anterior antennae, by the tail, or by these 
combined, but not I iy the other appendages except in con junction with either anterior 
antennae, or tail, or with both. 
7. Labidocera cestiva may attach itself to fixed objects in the water by the ante- 
rior antennae. It may also hang from the surface of the water by these organs. 
8. The anterior antennae perform at least three functions — mechanical orientation 
of the animal in falling, positive locomotion in leaping, and attachment to fixed 
objects or to the water film. 
9. Males and females react in characteristically different ways to light, 
gravity, etc. 
10. Females have a strong negative geotropism. Males have a weak negative 
geotropism. 
11. The geotropism of Labidocera is not changed by shaking it in water or by 
other forms of mechanical stimulation. Increasing the density of the sea water from 
1.025 to 1.035 and 1.050 increases slightly the negative geotropism of the males, but 
does not influence the females. Decreasing the density of the sea water from 1.025 
to 1.020, 1.015, 1.010, 1.005, and 1.000 does not influence geotropism. Temperature 
changes between 10° and 35° C. have no influence on the geotropism of the males. 
The geotropism of the females is negative in cold water and positive in warm, the 
critical temperature being about 26° C. 
12. Females have a strong positive phototropism for light of a low intensity. 
Males have a weak negative phototropism. The positive phototropism of the females 
is stronger than their negative geotropism. The phototropism of both sexes is 
unaltered by temperature changes between 10° and 35° C. It is also unaltered when 
the density of the sea water is varied from 1.050 to 1.000. Certain forms of mechanical 
stimulation (handling with a pipette, but not agitation in water) make females tempo- 
rarily negatively phototropic and increase the natural negativity of males. Females 
are negative to light of high intensity (100-candle power incandescent light at 10 
centimeters distance, and direct sunlight). Males are apparently indifferent to 
changes in light intensity. 
