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"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:

[ cells of the onion (allium cepa) ]

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 staining.

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 a tardigrade ]

Stomach region of an eutardigrade
with cell structures, overview.

[ stomach region of a tardigrade, detail ]

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:

[ echiniscus tardigrade ]

Echiniscus tardigrade, 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 division steps.

[ Echiniscus tardigrade eggs, first cell division stage ]

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.

[ Echiniscus tardigrade egg, four cell stage ]

Single echiniscus egg, after the second cell division, with four cells.

[ Echiniscus tardigrade egg, eight cell stage ]

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 for 'mulberry'.

[ Echiniscus tardigrade egg, multi cell stage. 'Morula' ]

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:

[ Echiniscus tardigrade egg, multi cell stage. 'Morula']

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 das Mikroskop.
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  (webmaster@baertierchen.de).
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.

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