108 
BULLETIN OF THE UNITED STATES FISH COMMISSION. 
made clear in two ways: First, when the animal hangs from the under side of a piece 
of glass the main axis of the body is nearly vertical, and thus the, other appendages 
are not in a position to touch the glass; and secondly, when animals anchor themselves 
to vertical surfaces of glass they do so quite as frequently by the dorsal surface of 
the body as by the ventral, and, since their appendages other than the anterior 
an ten use are on the ventral side, it follows that when they rest with the dorsal surface 
to the glass the only appendages that can touch the glass are the anterior antennae. 
How the antennas adhere to the glass is not certainly known, but it is quite probable 
that the attachment is accomplished by means of the numerous hairs that cover these 
organs and that are especially abundant at the tip. (Wheeler, 1900, p. 179, fig. 16c.) 
Not only can Labidocerae anchor themselves by their antennae to fixed objects in 
the water, but they can likewise hold to the surface of the water. A jar of water 
containing many Labidocerae can he so placed that the animals may be seen hanging 
from the surface of the water exactly as they would hang from the under surface of 
a piece of glass. To the surface of the water as to the glass the animals are attached 
by their anterior antennae. Slight waves are sufficient to dislodge them, but in quiet 
water great numbers hang in this way for considerable periods. 
The mechanism of attachment in this as in the former case has not been definitely 
ascertained, though it is very likely, as Scourfield (1900, p. 307) has suggested, that 
the hairs of the anterior antennae pierce the surface film of the water and produce 
capillary depressions by which the weight of the body may be supported. 
Thus, Labidocerae, whose weight ordinarily causes them to sink in sea water, 
overcome this tendency by gliding movements involving’ the action of their more 
centrally placed appendages, by leaps accomplished through the combined action of 
tail and anterior an ten me, and by attaching themselves through the anterior antennae 
to fixed objects in the water or to the surface film. In these operations the anterior 
antennae perform at least three functions: They orient the animal mechanically as it 
falls through the water, they are organs of positive locomotion in connection with 
the leaping habit, and, finally, they are organs of attachment while the animal rests. 
REACTIONS TO GRAVITY (GEOTROPISM). 
As already pointed out, most female and many male Labidocerae frequent the top 
of the water in any large aquarium much as the3 r do the top of the sea, and, as we 
have seen, they are continually falling from this situation because of the influence of 
gravity and as continually exerting themselves to regain it. Do the Labidocerae 
move toward the surface because it is nearer the source of light, i. e., are they posi- 
tively phototropic, or do they move in that direction because it is away from the 
earth’s center of gravity, i. e., are they negatively geotropic? 
To test this question a large glass tube about 8 centimeters in diameter and 
some 60 long, with one end open and the other closed, was set up vertically and 
nearly filled with sea water. On the side of the tube, and beginning at the bottom, 
five intervals of 10 centimeters each were laid off and marked, and the water in the 
tube was made to stand at the 50-centimeter mark. The apparatus was so arranged 
that the tube could be inclosed in a light-proof jacket without disturbing the con- 
tents by jarring, etc. 
The first experiment consisted in putting five female Labidocerae in the tube and 
recording their distribution under the influence of diffuse daylight. The sections in 
