326 ON THE MOVEMENTS OF THE DIATOMACEZ. 
and the thin glass cover of the live box. After a very 
short period of rest, the Pinnularia gave one or two . 
short jerking motions, and then the Cocconema began 
to move rapidly, broadside on, in a direction opposite 
to that pursued by the former (which remained sta- 
NAO EE 
~~ 
PRIS potters 
tionary) until it passed partly beyond it, when the , Ieee 
Pinnularia resumed its journey ; this was done twice Ey 
in precisely the same manner; on the third journey, FS 2 
it had changed its course, and passed beyond the ob- a 
structing valve. The arrow indicates the direction 
in which the Pinnularia was moving. The Cocconema 
was of course forced in the opposite direction. Now, 
a result very similar to these might be produced 
by the expulsion of a fluid from the Diatom valve, 
according to Professor Smith’s theory, but the orifices through which 
it would require to be forced would have to be placed along the side 
of the valve as well as at either end. And not only would this be 
necessary, but two sets of orifices, pointed in opposite directions, 
would be essential, in order to produce the double motion, backwards 
and forwards. While two sets more would be required to produce 
the motion I have before described, when the diatom saw fit to change 
its course. And besides all this elaborate mechanism, another must 
still be added, by means of which every opening would be completely 
closed but those for the moment employed in producing the motion 
In one given direction. 
If this really is the correct solution of the question, the motion 
then of the Diatomacee is unique, for I doubt if any thing anala- 
gous to it can be found in nature. But if the presence of cilia be 
granted them, then there is no difficulty in at once understanding how 
every movement of the diatom valve can be readily produced merely 
by changing the direction of the ciliary motion. The objection urged 
by Professor Smith, that by colouring the water, no motion in the 
particles of the colouring matter could by him be detected, if it isa 
valid one against ciliary action, it is equally fatal to his own theory, for 
in his way of accounting for the motion, a current must be produced, 
but he has never seen any, or been able to detect it, and from this, he 
concludes there are no cilia. Let us reverse Professor Smith’s argu- 
ment, and the case will stand thus :— 
If the motion is caused by the expulsion of a fluid from the 
ee 
71 ACYU 
