106 
BULLETIN OF THE UNITED STATES FISH COMMISSION. 
animals sink in sea water, and sink at a considerable rate. The time taken by each 
of 10 etherized individuals to fall through 20 centimeters of sea water varied from 
35.2 seconds to 17.2 seconds, and averaged 40.7 seconds. The rate of fall over 
different parts of the course seems to have been rather uniform, for in a second series 
of observations the first 10 centimeters were passed over in an average of 21.68 
seconds, and the second 10 in 18.58 seconds, giving a general average for the whole 
20 centimeters of 40.26 seconds. From this and the preceding observations it is fair 
to assume that the animals fall through the water at the average rate of about half a 
centimeter a second. They would thus drop a fathom in about six minutes. 
The positions that the animals assume in falling through the water are different 
in different cases. When they are killed suddenly by adding a small amount of alco- 
hol, formaldehyde, or corrosive sublimate to the water, and are then transferred to 
ordinary sea water, they descend head downward. When, however, they are placed in 
water containing a small amount of ether and are thus made motionless without being 
killed, they fall through ordinary sea water with the head uppermost. This, too, is 
the position assumed by the living animals when descending. The difference in the 
mode of descent of the dead and of the etherized animals is due to the disposition of 
the appendages. Strong killing reagents, such as alcohol, formaldehyde, etc., act so 
vigorously on the animals that they die with all their muscles contracted. Since the 
flexors are stronger than the extensors, the appendages, and particularly the anterior 
antenna?, are folded alongside the body in death and the animal moves head first 
through the water, probably because of the greater specific gravity of the head. In 
the etherized and the normal animals, on the other hand, the anterior antennas are 
kept spread and the resistance that they meet in their passage through the water 
retards the falling of the head so that the animal descends with the head uppermost. 
This is of no small importance to a living Labidocera, for, being thus oriented in its 
fall, its first efforts at locomotion must be effective in carrying it toward the surface. 
Thus, irrespective of other functions that have been ascribed to the anterior antennae, 
the} 7 undoubtedly serve as organs for the orientation of the body. It is not without 
interest to recall that the function of orientation in the higher crustaceans is also 
dependent, in part at least, on the anterior antennae, although in these forms this 
function is connected with a special sense organ, the statocyst, whereas in the Labi- 
docerae the antennae as a whole probably act in a purely mechanical way. 
What has been said about the movements of female Labidocerae applies also 
to the males, except that in their locomotion this sex often does what the other rarely 
attempts, namely, swims downward. Thus the males gain a much moi’e general 
distribution than the females. 
In both males and females the kinds of locomotion, except for direction, are much 
the same. Both sexes at times exhibit a uniform continuous movement, as though 
the animals were creeping rapidly through the water; at other times, and this is the 
more usual, they pass through the water by relatively enormous leaps, carried out at 
such high velocities that it is sometimes impossible to follow the animal with the eye. 
Although intermediate forms of locomotion occur, such as a succession of short leaps, 
the majority of movements belong to one or other of the two kinds just described. 
The leaping movements of the copepods have been usually ascribed to the vigor- 
ous action of the anterior antennae. Recently MacBride (1899, p. 505) has called this 
opinion in question and has maintained, on the grounds of observations on the slower 
leaping movements, that the leap is effected entirely by the simultaneous action of 
