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ORIGINAL COMMUNICATIONS.
On the OCCURRENCE among the INFUSORIA of peculiar ORGANS
resembling THREAD-CELLS. By GEORGE J. ALLMAN, M.D.,
F.R.S. (With a Plate.)
(Read at the Meeting of the British Association at Liverpool, Sept. 1854.)
IN an important monograph by Cohn on the Paramcecium
Bursaria,* this author maintains that the cilia with which the
whole surface of the animalculae is covered are in reality much
longer than their appearance in the living animal would lead
one to believe. He founds this opinion on the fact, that
when the animal is allowed to dry on the glass object-holder
it is seen to bristle with long rigid filaments, which he believes to be the cilia, really unaltered in length, though then
for the first time become visible in their entire course; and,
in accordance with this view, he figures the Paramwcium
covered with cilia very much longer than the inspection of
the living animal alone would justify.
Stein, in his remarkable work on the development of the
Infusoria,f refers to this opinion of Cohn, whom, however, he
considers in error, in supposing the long bristle-like processes of the dead animalcule to represent the natural length
of the cilia in the living. He maintains on the contrary that
these processes are the cilia abnormally lengthened under external influences; and he states that he has witnessed the
same phenomenon in many other Infusoria in which he has
always been able to induce it by the application of strong
acetic acid, when the cilia suddenly extend themselves to
three or four times their original length.
While recently engaged in examining the structure of a
nearly allied animalcule, the Bursaria leucas, Ehr.—a green
variety of which was developed during the present autumn in
great profusion in a small pond in the county of Essex—I
witnessed an appearance exactly similar to that described by
Cohn and Stein; but it soon became clear to me that the
German naturalists had erred in their explanations of it; and
I am now satisfied that the filaments in question have nothing
whatever to do with the cilia, but are peculiar and very remarkable organs, hitherto undescribed in the Infusoria.
When this animalcule is examined under a sufficiently
* Siebold u. Kblliker Zeitschrift, Bund III. 260.
t Die Infusionsthiere auf ihre Entwickelungs gesohichte. (' QuarterlyJournal of Microscopical Science,' Vol. ii., p. 272.
VOL. III.
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ON SOME PECULIAR ORGANS OF THE INFUSORIA.
high power, minute fusiform bodies may be detected thickly
imbedded in its walls. (Figs. 11 and 12 and 14 h, Plate X.)
These bodies are perfectly colourless and transparent; they
are about the l-2500th of an inch long, and may easily, even
without any manipulation, be witnessed at the margin, where
they are seen to be arranged perpendicularly to the outline
of the animalcule, while on the surface turned towards the
observer their extreme transparency and want of colour render
them invisible against the opaque back-ground, and it becomes
necessary to crush the animalcule beneath the covering-glass
so as to press out the green globules which it contains, in
order to bring the fusiform bodies into view. To these bodies
I propose to give the name of trichocysts.
As long as the animalcule continues free from annoyance,
the trichocysts undergo no change, but when subjected to external irritation, as occurs during the drying away of the surrounding water, or the application of acetic acid or other
chemical irritant, or the too forcible action of the compressor,
they become suddenly transformed into long filaments, which
are projected from all parts of the surface of the animalcule
(fig. 13) ; and it is these filaments which, being mistaken for
cilia by Cohn and Stein, gave rise to the erroneous views just
mentioned.
The rapidity with which this remarkable change is effected,
joined with the great minuteness and transparency of the object, renders it extremely difficult to follow it, and for a long
time I could only satisfy myself of the fact that the fusiform
bodies were suddenly replaced by the projected filaments.
After continued observation, however, I at last succeeded in
witnessing the principal steps in the evolution of the filament.
It is not difficult, by rapidly crushing the animalcule, to
foroe out some of the trichocysts in an unchanged state.
(Fig. 15.) If the eye be now fixed on one of the isolated trichocysts, it will most probably be seen after the lapse of a
few seconds to become all at once changed with a peculiar
jerk, as if by the sudden release of some previous state of
tension, into a little spherical body. (Fig. 16.) In this condition it will probably remain for two or three seconds longer,
and then a spiral filament will become rapidly evolved from
the sphere, apparently by the rupture of a membrane which
had previously confined it, the filament unrolling itself so
quickly that the eye can scarcely follow it (fig. 17), until it
ultimately lies straight and rigid on the field of the microscope, looking like a very fine and long acicular crystal.
(Fig. 18.)
GLAISHER, ON SNOW CRYSTALS.
179
T h i s remarkable body when completely evolved (fig. 18/.)
consists of two portions—a rigid spiculum-like portion acutely
pointed at one end, and continuous at the opposite end with
the second portion, which is in the form of an excessively fine
filiform appendage less than half the length of the spiculum :
this second portion is generally seen to be bent at an angle on
the first, and is frequently more or less curved at the free end.
The form of the evolved trichocysts is best observed in such
as have floated away towards the margin of the drop of water,
and are there left dry by the evaporated fluid. In many of
them the filiform appendage was not visible, and they then
merely presented the appearance of a simple, long fusiform
spiculum. (Fig. 18 k.)
The resemblance of the organs now described to the wellknown thread-cells of the Polypes, and of certain other lower
members of the animal kingdom, is obvious. That they are
entirely homologous, however, with these bodies we can
scarcely yet assert. Their origin, at least, appears to be
different; for if we admit the unicellular structure of the
Infusoria, we have the trichocysts apparently developed in the
substance of the cell-wall, instead of being produced in
special cells, as we know to be the case with the thread-cells
of the Polypes.
SNOW CRYSTALS in 1855.
By J. GLAISHER, Esq., F.R..S.
(Read before the Greenwich Natural History Society.)
THK many snow crystals which fell during the late severe
weather, attracted such general attention, that I ventured to
announce a paper on the subject for the present evening.
Never do I recollect such an infinity of crystals as have lately
fallen beneath my observation. Generally speaking, they fall
at rare intervals and very sparingly, in cold and calm weather,
and frequently at the commencement of a thaw. In the
present year they have fallen under all circumstances of wind
or calm, with snow, and alone, during the continuance of the
late severe weather when the temperature varied from a few
degrees above zero to the freezing point, and up to the precise
moment of the thaw, with a temperature of from 34° to 37°. The
size of these beautiful objects was by no means unappreciable,
and might be said to vary from 0 • 05-inch to 4-10ths of an
inch in diameter. Their forms were so varied, that it seemed
scarcely possible for continuous observations to exhaust them
all. I therefore endeavoured to secure observations of those
which might be considered types of their class, trusting to a
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