"A telescope can resolve a faint spot
down to crisp, individual stars - but this is a rather weak pleasure when
compared to the delight of a microsocope resolving everything around us
into this fabulous world of cells ..."
Gustav Jäger (1867)
... the fabulous world of cells - some among you will be reminded of
their childhood and in particular of those biology lessons where an
onion (allium cepa) was brutally torn into pieces and investigated under
a microscope in order to demonstrate the existence of ubiquituous cell
structures which are common to all so-called higher organisms:
Original, temporary preparation of
an onion shell, prepared for a school lesson in biology.
Cell walls and cell nuclei become clearly visible by help of a little bit of blueish
The discovery of the cell as an elementary biological unit is commonly
attributed to Robert Hooke (1635-1703). In his famous 'Micrographia' (1667)
Hooke described typical vegetable cells, using cork cells as an example.
Though our tardigrades are really tiny they consist of many cells as well,
typically a few hundred cells. Normally the cell walls cannot be easily
perceived when looking at the living tardigrades. But from time to time,
depending on the tardigrade species, tardigrade age, health and illumination,
typical cell structures can become visible without any preparation
and without staining:
Stomach region of an eutardigrade
with cell structures, overview.
Detail from the image above,
with clearly visible,
polygone type cells.
In other cases we are often not able to distinguish those cell structures.
We do notice marvelous, fine details like legs with delicate claws, cute noses
and much more but there might be a complete lack of any kind of cell characteristics:
dark field illumination. The complex and optically dense structure doesn't
reveal any cell structures.
Well, what should we do now? Should we stop all tardigrade cell investigations
and return ruefully to the onion shells?
We can continue our tardigrade cell structure investigations also with those
Echiniscus tardigrades. We just have to look at the tardigrade eggs and
in particular at the timeline of egg development.
A freshly deposited tardigrade egg might be still in the one-cell stage when
we happen to come across it. Its fine structure looks rather homogeneous,
with a little bit of yellowish grain in it. But keep in mind that this
it not just some kind of brainless stuff but a biological clockwork
programmed to create a perfect microscopical tardigrade with a wide
variety of nano-sized mechanisms in it.
With a little bit of patience we can easily study the first cell
Exuvium (group of deposited eggs) by an
Echiniscus tardigrade. The first cell divisions have happenend simultaneously
ending up in two cells of the same size each.
Single echiniscus egg, after the second cell division,
with four cells.
Single echiniscus egg, after the third cell division,
with eight cells.
The cell divisions continue, 16, 32, 64 and 128 cell stages follow, possibly
not always exactly simultaneously, until it is no more possible to tell the exact number
of cells. This stage is called a "Morula" which is the Latin term
Single egg of an Echiniscus tardigrade, multi cell stage 'Morula'.
Once you will have seen one of those multi-cell stages you will be
able to recognize it in other situations as well:
Eggs of an Echiniscus tardigrade,
in multi-cell stage.
Of course, at some moment the development of cells must
turn into differentiation. Otherwise we would end up with a stupid
snowball of identical cells and not with a fully developped tardigrade.
But this will be the subject of a latter issue of our magazine.
In any case this miraculous process seems to happen in a perfect manner
billions of times per year, without asking the advice of one of our
constantly wise business consultants - strange, isn't it?
Gustav Jäger: Die Wunder der unsichtbaren Welt enthüllt durch
P. 39. Berlin 1867.
Rudolf Väth: Robert Hooke und die "Micrographia".
Mikrokosmos 88 (1999) p. 129 - 138.
© Text, images and video clips by
Martin Mach (email@example.com).
Water Bear web base is a licensed and revised version of
the German language monthly magazine Bärtierchen-Journal .
Style and grammar amendments by native speakers are warmly welcomed.