28 On Syncheta Mordaz. oS 
dropped some living specimens into different solutions of bi-chro- 
mate of potash, and I soon found that the potash required to be 
diluted extremely in order to kill the creatures with sufficient slow- 
ness. In a solution of 1 in 500 of the volumetric solution of 
bi-chromate of potash they would live for about twenty-four hours, 
and die very gently and gradually. I had adopted this plan in the 
hope that the animal would remain naturally extended after death, 
and that I might then be lucky enough in the compressorium to get 
it into the desired position; but on looking at the rotifers after about 
twenty-four hours’ immersion, I saw one swimming very slowly and 
upright; I at once slipped the trough under the microscope and 
had at last the pleasure of seeing the head which had go long baffled 
me: Fig. 2 gives this view of Synchata. About ten minutes after 
I began my examination the animal died, and I have found on re- 
peating the experiment that the rotifers in the solution must be 
looked at every now and then before the twenty-four hours have 
expired, as some will live quite an hour or two longer than others, 
and as all of them, when they have once reached the stage of feebly 
swimming upright, soon die: moreover, quite half of them perversely 
die without gomg through the ceremony at all. 
To return to the methods by which the ciliated lobes produce 
Synchexta’s motions. Fig. 3 shows one of the lobes with the cilia 
on it at rest. The cilia strike the water one after another in turn, 
generally giving a vigorous downward blow and then gently return- 
ing to the position they started from. When these motions take 
place in planes at right angles to the base of the lobe, they will 
clearly produce an onward movement in the animal in direction of 
its length. Should the planes in which the cilia move be oblique 
to the base of the lobe, the effect will be not only to produce an on- 
ward movement, but to throw the animal constantly out of the line 
of its own length in a direction at right angles to those planes; the 
result would be a corkscrew path such as Syncheta habitually swims 
in; but if when these planes are at right angles to the base of the 
lobe the cilia were to strike an upward blow as vigorous as the 
downward one, the creature would be kept slightly oscillating over 
the same spot, as the two blows would neutralize each other. 
It is by a similar process that a fly hovers in the air, as may 
easily be seen in the common wasp-like flies in our gardens ; for on 
approaching them closely it will be seen that they seem to have four 
wings (though really possessing only two), owing to the rapidity 
with which the backward stroke is instantly balanced by a forward 
one, and the comparatively longer interval of time which follows 
each pair of strokes. 
If the ciliated lobes are looked at from above when the animal 
is erect, it will be seen that owing to the cilia beating regularly in 
turn, a series of waves producing a wheel-like appearance runs round 
