BOTATOBIA OF THE UNITED STATES. 
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mass. In living specimens the reservoirs are entirely clear, and have often been 
taken for the contractile vacuole, occupying as they do the position usually taken 
by the vacuole in other rotifers. 
One of the two reservoirs opens at the base of the right toe, the other at the base 
of the left toe (see fig. 6, pi. I, and fig. 69, pi. vm). The tenacious secretion passes 
out between the base of the toe and the substyles, being directed by the latter down 
along the surface of the toe. From the tip of the toe it trails off into the water, like 
a spider’s web, and attaches itself to any object with which it comes in contact. The 
animal then remains suspended in the water, like a spider from its thread (though 
of course the rotifer, owing to the movement of the cilia, may hang upward or hori- 
zontally, as well as downward). The animal spins about on its long axis, remaining 
nearly in the same position, or it may of course move in the circumference of a circle 
about the object to which it is attached. 
While thus attached, the action of the cilia brings food to the mouth, just as in 
the Rotifera that are permanently fixed by their posterior ends. The free- swimming 
Rotifera which have this secretion of mucus have thus the advantage of being able 
to temporarily change their roving method of life into a fixed one. 
But the thread produced by the mucus is not so strong, apparently, but that by 
an extra effort it may be broken at any moment. Often a specimen will be seen to 
swing about from its point of attachment for a considerable time, then suddenly to 
start rapidly forward, swimming with the most complete freedom. Often too the 
mucus seems to act merely as a yielding thread — moderating the course of the 
animal a little — but being drawn out as the animal progresses. 
Sometimes the mucus becomes a trap which results in the death of the animal. 
A specimen will sometimes bring the base of its toes against some solid object, as 
the glass slide on which it is undergoing examination, at the moment when a large 
quantity of the mucus has been given out, It thereupon sticks fast, perhaps by the 
entire length of the toe, to the glass and can not escape. It then remains attached 
at this point till it dies. It is probable that such an accident rarely occurs except 
when the animal is under such unusual and cramped conditions as it finds between 
the slide and the cover-glass. 
In Diurella tigris Muller, in which the two toes are equal, the two reservoirs are 
also equal (pi. I, fig. 6). But in most species in which the right toe has become 
rudimentary, the right reservoir has likewise much decreased in size. This is the 
case, for example, in Rattulus bicristatus G-osse (pi. ix, fig. 79) and R. longiseta 
Sch rank (pi. vm, fig. 69). In R. stylatus Gosse, however, the two reservoirs are 
still nearly or quite equal in size (pi. x, fig. 92), although the right toe has nearly 
disappeared. 
THE ASYMMETRY OF THE RATTULIDA3 AND ITS BIOLOGICAL SIGNIFICANCE. 
The writer has already given in a separate paper" a general discussion of the 
significance of asymmetry in a number of lower organisms, so that only the salient 
points, with their application to the Rattulidce, will be set forth here. 
All the Rattididce. are more or less unsymmetrical in their structure. If we seek 
for a general statement which shall express the nature of this asymmetry we shall 
find it most fully set forth as follows: Conceiving the middle to be a fixed point, the 
« Asymmetry in Some Lower Organisms and its Biological Significance. Mark Anniversary Volume, N. Y., 1903. 
