Encyclopaedia Britannica > Volume 3, Anatomy-Astronomy

ANIMALCULE.
- crush the specimens, when the coloured fluid will enter and
surround their bodies ; and, by a proper and expert manage¬
ment of the illumination of the microscope, the broken edges
of the lorica will become visible.
The unfixed condition of opinion regarding infusorial ani¬
malcules is curiously indicated by the fact, that many care¬
ful and assiduous observers, such as Bauer, Leuckhart, Agas¬
siz, and Reichenbacb, deny the very existence of these
creatures as a class, and maintain that they are mostly the
embryonic forms of other and more highly organized beings.
We doubt not that the opinion expressed in our preceding
article, that our knowledge of this “ invisible world” is in
its infancy, is still correct, and that as the telescope brings
forth stars from their nebular darkness, so the further the
light of our microscopic knowledge penetrates into the ob¬
scure depth of the animalcular kingdom, the more clearly we
shall have its now component parts resolved into definite
forms of another nature than we at present suppose them.
But that they are all merely embryonic forms, is doubtless
a most visionary view, as no reason can be assigned a priori
that beings, however small, are either uncertain or transi¬
tional, or that completion and finality of form are in any way
inconsistent with excessive minuteness. One lesson may
assuredly be drawn from the difficulties which beset the sub¬
ject,—to avoid dogmatism, and bear in mind how unable we
often are to solve the question, “ What is truth ?” But the
extraordinary mutability of form and outward aspect of those
frail creatures is no argument against their fixity of specific
character within a certain range of variation, however wide.
We know how different are the individuals even of some of
the higher species from each other, under different circum¬
stances, and at different stages of their life; but when once
under our eye, they may be made cognizable to the senses
of an observant person, under all their phases ; that is, they
may be identified with certainty from time to time. But
with many annnalcular beings it is not so. We see them
once, as the astronomer may see some “ bright particular
starbut we cannot calculate their erratic and changing
course of life; and thus they may be either seen again no
more for ever, or be observed under an altered aspect by
another observer, and recorded with new characters under a
different name. These, and such-like causes, may easily be
conceived to operate disadvantageously against our speedy
acquirement of assured knowledge regarding the animalcular
tribes. But by means of patient and discriminating investi¬
gation on our own parts, a candid consideration of the ob¬
servations of others, and an unbiassed record of whatever
has been clearly ascertained, there is no reason why the sub¬
ject should not be gradually advanced so as to take rank with
other branches of a less ambiguous nature. The general
211
reader will not wonder at the state of uncertainty which still
pervades our notions of many animalcules, when we mention,
ai? efTr.nPle °P extreme minuteness, Monas crepusculum,
of which the number occupying the space of a grain of mus¬
tard seed, one-tenth of an inch in diameter, has been calcu¬
lated at eight millions !
Ehrenberg’s great group of polygastric animalcules is pri¬
marily divided into Anentera (such as do not possess a true
alimentary canal), and Enterodela (or such as are furnished
with an alimentary canal). Here we are met by a noted an¬
tagonistic observer upon the very threshold.
“ Recent investigations,” says M. Agassiz, “ upon the so-
called Anentera, have satisfactorily shown, in my opinion,
and in that of most competent observers, that this type of
Ehrenberg’s Pohjgastrica, without gastric cavities, and with¬
out an alimentary tube, are really plants belonging to the
order of algae in the widest extension of this group; while
most of the monad tribe are merely moveable germs of
various kinds of other algae. As for the Enterodela—most
of them, far from being perfect animals, are only germs in
an early stage of development. The family of Vorticella
exhibits so close a relation with the Bryozoa(cilio-brachiate
polypes), and especially with the genus Pedicellina, that I
have no doubt, that wherever Bryozoa should be placed,
Vorticella should follow, and be ranked in the same division
with them. The terminal group of Infusoria, Bursaria,
Paramecium, and the like, are, as I have satisfied myself
by direct investigation, germs of fresh-water worms, some
of which I have seen hatched from eggs of Planaria laid
under my eyes.”1
Not only are authors on our present department opposed
to each other, but (a rarer case) they seem in some instances
to have no great confidence even in themselves. Thus M.
Dujardin, one of the most trustworthy of the modern micro¬
scopic observers, after giving in a tabular form the charac¬
ters of the groups which constitute the family Monadina,
sums up by stating : “ But these generic distinctions are
entirely artificial, and simply intended to facilitate the nam¬
ing of Infusoria one may meet with in such and such in¬
fusions, and which, when better known, may prove in some
instances to be but varieties of a single species.”2
The preceding notices will suffice to show the still unset¬
tled state of opinion regarding animalcules, and that Ehren¬
berg’s system, although of great importance to the discrimi¬
nating student, is not to be adopted implicitly as an assured
exposition of the truth. We cannot here exhibit more of his
arrangement than a compendious view of the family groups,
—referring for details of genera and species to the work it¬
self,3 and to others, with a list of which we shall conclude these
supplementary observations.
Anentera,
without true
Alimentary
Canal.
No foot-like
appendages.
Gymnica.
With variable
foot-like processes.
Pseudopoda.
Hairy.
Epitricha.
Tabular View of Ehrenberg's Arrangement.
Self-division ( illoricated, or without shell
complete, j loricated, or shelled
V illoricated
Self-division selfld.iv.is.ion general and globular
Form of body
constant.
incomplete, j sel^11” | illoricated.
■ v l (filiform).... I loricated..
I Form of body 1 illoricated
\ variable. J loricated
illoricated
•i • + j / Foot-like processes, compound
onca e j Foot-like processes, simple
f illoricated
\ loricated
Family.
Monadina.
Cryptomonadina.
H ydromorina.
Yolvocina.
Yibrionia.
Closterina.
Astaseea.
Dinobryina.
Am<eba:a.
Arcellina.
Baciblaria.
Cyclidina.
Peridinasa.
1 Annals of Natural History, vol. vi. p. 156, 1850. Similar observations had been made by Mr Girard, who states that Kolpoda cu-
cullus is an embryonic stage of a species of Planaria. 2 Hist, des Infusoires, p. 273.
3 Hie Infusionsthierchen als vollkommene organismen. Ein Blick in das tiefere Leben der organischen Natur. Atlas mit 64 illummirten
Kupfertafeln, gr. fol. Leipzig, 1838.