December 1898] THE MOVEMENT OF DIATOMS 407 
the walls of the cleft approach one another very closely in such a 
manner as to simulate the appearance of an internal closure. In 
those examples in which the cleft, seen in transverse section, has an 
angular course, O. Miiller considers it probable that the central 
portion is closed during life by the middle lamina, in which case 
two canals would persist, one running along the outer surface, the 
other along the inner surface of the cell-wall, but Lauterborn 
has not observed such a closure, nor does he consider its occurrence 
probable. This is of some importance, since Miiller postulated the 
presence of such canals in his theory of the movements of diatoms. 
As to the transverse markings (Riefen) of the frustule, Lauter- 
born’s results are entirely in agreement with those of Flogel, who had 
previously described the appearances as being, in reality, chambers 
hollowed out in the substance of the frustule, and communicating 
by a tolerably wide opening with the interior of the cell. These 
features are well shown in Fig. 1, where the plane of section passes 
through four of these chambers, and Fig. 2, which is an outline 
drawing of a section passing between two chambers in one valve of 
the frustule. These drawings also illustrate the way in which the 
two valves are united by the overlapping of their free edges. 
The interior of the cell is lined during life by a layer of proto- 
plasm, thinner laterally than elsewhere, and, in the middle of the 
cell, forming a transverse bridge-like mass containing the nucleus. 
On each side of this central portion the peripheral protoplasm 
surrounds a large vacuole filled with cell-sap. This condition of 
things suggested to Lauterborn a possible explanation of its meaning, 
which, although purely hypothetical, is worth consideration. 
The researches of O. Miiller have shown that the protoplasm of 
Pinnularia is subjected to a very considerable osmotic pressure 
(4 to 5 atmospheres), manifested with equal intensity in all direc- 
tions. Now pressure in the direction of the lateral walls would 
result in pressing the overlapping elements closer together, but 
when exerted at right angles to this, in the direction of the raphe, 
there would be a tendency to force the two halves of the frustule 
apart, if the frictional resistance of the overlapping elements was 
not sufficient to maintain equilibrium. But, as we have already 
seen, on each side of the raphe internally a great number of 
transverse chambers are placed one behind the other, and filled by 
prolongations of the peripheral protoplasm that enter each chamber 
by an opening about half the diameter of its internal cavity. 
Lauterborn suggests that these chambers filled with abstricted 
portions of the protoplasm might be imagined to act as so many 
clamps (‘ Klammern ’) opposing a strong resistance to the force tending 
to separate the two halves of the frustule, and so strengthening the 
frictional resistance of the overlapping elements. He points out 
