ing the fluid with carmine or indigo, been able to detect in the
coloured particles surrounding the Diatom, those rotatory movements
which indicate, in the various species of true infusorial
animalcules, the presence of cilia. I am constrained to believe
that the movements of the Diatomaceæ are owing to forces
operating within the frustule, and are probably connected with
the endosmotic and cxosmotic action of the cell. The fluids
which are concerned in these actions must enter and be emitted
through the minute foramina at the extremities of the siliceous
valves ; and it may easily be conceived, that an exceedingly small
quantity of water expelled through these minute apertures
would be sufficient to produce movements in bodies of so little
specific gravity.
If the motion be produced by the exosmose taking place alternately
at one and the other extremity, while endosmose is proceeding
at the other, an alternating movement would be the
result in frustules of a linear form ; while in others of an elliptical
or orbicular outline, in which foramina exist along the entire
line of suture, the movements, if any, must be irregular,
or slowly lateral.
Such is precisely the case. The backward and forward movements
of the Naviculeoe have been already described ; in Surirella
and Campijlodiscus the motion never proceeds farther than a languid
roll from one side to the other ; and in Gomphonema, in
which a foramen, fulfilling the nutritive office, is found at the
larger extremity only, the movement is a hardly perceptible
advance in intermitted jerks in tbe direction of the narrow end.
The subject is, however, one involved in much obscurity, and is
probably destined to remain, for some time to come, among the
mysteries of nature, which baffle while they excite inquiry.
S e c t io n V.
S e l f -d iv i s io n in t h e D ia t o m a c e æ .
This process, by which a single cell is converted into two perfect
cells, is by no means peculiar to the Diatomaceæ, but prevails
extensively in the vegetable kingdom, if indeed it bo not
the ordinary mode of increase in all such tissues. Certain it is,
that ill the great class of unicellular Algæ, it is the universal
mode of growth and multiplication. It, however, presents several
peculiarities in the organisms with which we are now concerned,
and is also so readily noted and followed in all its stages in the
Diatomaceæ, that a close observance and clear comprehension
of the process in their case may illustrate and guide inquiry in
other tribes.
The first step in the process of self-division in the Diatomaceous
frustule, is the fission of the internal cell, probably by
the doiibling-in of its membranous wall, and consequently the
separation of the endochrome or cell-contents ; the central vesicle
or cytoblast also dividing into two parts, which remove to a little
distance from each other ; these movements being simultaneous
with a retrocession of the epidermal valves and the formation of
the siliceous connccting-membraiie already described. In the
centre of the enlarged frustule, in exact apposition to the original
valves, and closely applied to them, there are now formed two
new valves, covering the surface of the cell-membranes along the
line of fission. The divided portions of the endochrome spread
themselves along the membrane which is embraced by the new
valves, and there result two half-new frustules, bound together
by the connecting-membrane, generated during the process we
have described. The figures of self-division given throughout the
plates will serve to illustrate this description ; and more especially
those in PL VIII. fig. 5 9 i, PL XV. fig. 126 d, PL XXII. fig. 216 d.
During the healthy life of the Diatom, the process of selfdivision
is being continually repeated ; the two half-new frustules
at once proceed to divide again, each into two frustules,
and thus the process continues. I have been unable to ascertain
the time occupied in a single act of self-division ; but supposing
it to be completed in twenty-fom- hours, we should have,
as the progeny of a single frustule, the amazing number of one
thousand millions in a single mouth : a cn-cumstaiice which will
in some degree explain the sudden, or at least rapid, appearance
of vast numbers of these organisms, in localities where they were,
but a short time previously, cither mirecognizcd, or only sparingly
diffused.