1897 | THE MOVEMENTS OF DIATOMS 41 
glass. It happens sometimes that the movement of translation 
is stopped for a while, after which the cell seems to make efforts 
to pluck itself away from the substratum and then runs forward, 
only to stop again after a little course and to repeat this play 
again. 
And sometimes the cell, stopped in its movement, goes away 
from the substratum, being retained only by a small gelatinous 
cushion sticking to the cover glass, and performs small oscilla- 
tions in that position. It makes the impression that the osmotic 
currents between the cell and the surrounding water are too 
weak to overcome the resistance of the adhesive mucus, and 
cause these oscillations. 
Pfitzer, in his interesting study upon Bacillariacee in Schenck’s 
Handbuch der Botanik, has raised a theoretical objection against 
the osmotic theory of movements. He suggests that the low 
velocity of the osmotic current cannot furnish sufficient force to 
account for the forward motion of the cell. The objection 
really is based upon a misunderstanding; for in all movements 
“ produced by flowing out of liquid from a vessel (or flowing into 
it) the cause of the movement does not lie in the velocity of the 
current, but exclusively in the change in the position at the cen- 
ter of inertia, and it is equally true whether the liquid flows out 
through macroscopical or molecular openings. 
We then have no reason to put aside the endosmotic hypoth- 
esis of movements, inasmuch as no observation has proved the 
existence of plasmatic pseudopodia or other organs for creeping ;° 
and, moreover, that hypothesis gives us the basis for the expla- 
nation of some peculiarities of these very enigmatic movements. 
The movements of the Diatomacee were very precisely 
described by the late E. Borscow,’ who discerns three types: 
first, sliding ; second, creeping ; third, the above described inter- 
mittent movement or leaping. 
The most characteristic are the sliding or peta: move- 
considered as flagella are simply alien fungi. “The pseudocilia,” says he, “are 
A der Riefenkammern.” /éid. 14:58, 59. 1896. 
7 Die Siisswasserbacillariaceen des a Russland. Kief. 1875. 
