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In the last issue we have seen that some tardigrade species deposit their eggs freely, just as in the example shown below.

[ tardigrades: eggs ]

Three eggs deposited by a water bear of the genus Macrobiotus, sticking together.
Egg diameter about 90 µm.

Other species leave their eggs in the old cuticula (skin) after moulting. So the old skin still serves as a shelter for the eggs.

[ Tardigrades: Eggs deposited by Milnesium tardigradum ]

Nest of four tardigrade eggs in old skin.  In the eggs on the very left side and on the very right side you will perceive the two bent stilettos close to the buccal tube.

Are you interested in more precise information? Water Bear web base is intended to be a popular magazine, nevertheless we might peep over to the real scientists for a moment. Much of the knowledge at hand today has been available already about 100 years ago. As an example we might choose a short text block published in 1936 by the famous Berlin tardigrade specialist Ernst Marcus. There are a lot of scientific terms included and it might be helpful to have some of your biology school textbooks at hand before beginning. I have worked hard to translate all this from German and I hope that the contents are still there:

"Egg formation proceeds by means of nutrimentation by abortive egg cells. The ovary endothelium forms a chorion as an egg shell. It is important for taxonomic reasons to know whether the egg shell is smooth or has so-called egg processes (typical for the genus Macrobiotus). Adequate furrowing proceeds irregularily by phase difference. The diploid chromosome number ranges from about 10 to 14. Gastrula formation is performed by endoblastic delamination. Gametes can be seen at first within the primary entoderm. By folding away from the archenteron 5 metamere pairs of coelom containers are formed. The first four pairs of those coelom containers dissolve and produce muscles and storage cells. The fifth pair forms the gonades and the gonade tubes. The stomadeum including stylets and the muscles of the buccal tube, buccal glands, intestinal glands, proctadeum, claw formation glands and the nervous system which is split off from the epidermis, are all ektodermal. The middle part of the intestine is entodermic. The extremities are processes of the body wall."

(Ernst Marcus: Tardigrada. p. 14. Berlin 1936)

Now you have encountered a poor translation from the German original by the author of the  Water Bear web base  magazine. So, possibly you were not able to understand everything in detail. Nevertheless this example should have helped to make clear that tardigrade egg development investigation was on a high level already in the first half of the 20th century. You can even go back further on the timeline and find several series of colour prints of tardigrade egg cross sections in the professional literature as early as in the late 19th century! It is a pity that those splendid works have been superseeded by time and cannot be found any more in modern bibliographies.

[ Tardigrades: Egg deposited by Milnesium tardigradum]

Tardigrade embryo.
Cross section picture after Ernst Marcus: Tardigrada. Berlin 1929.

kc: head coelom container;
md: middle part of intestine;
pd: proctadeum;
rc1-rc4: first to fourth coelom container;
sd1: salivary gland formation center ;
sd2: buccal apparatus.

For those among you who might consider all this as too scientific and theoretic I will comment on the terrific film

!!!   Young tardigrades moving eagerly within their eggs !!!

It is not so time consuming (about three seconds) and it is free for ages zero and up:

Just click here

In the next issue we will be virtual witness to a famous historical situation when Privy Councillor professor C.A.S. Schultze, discoverer of the tardigrade Macrobiotus hufelandi, poured some water on a small sample of sand and mud. This was an experiment in front of a scientific audience and intended to convince the doubtful conservative scientific authority, professor Ehrenberg, that tardigrades can find back to active life from a completey desiccated, death-like state.

© 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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