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> Hydras are very simple tubular animals with a thin layer of cells, a tubular body with tentacles that sting, and can regenerate themselves from a bit of body:
> 
> https://www.nytimes.com/2017/02/13/science/hydra-regeneration-video-scitake.html?emc=edit_th_20170221&nl=todaysheadlines&nlid=60788861&_r=0
> 
> "The hydra is a favorite subject of middle school science. It is a fearsome-looking tentacled predator, but it is tiny — less than a half inch — and lives in ponds. You can collect or buy hydras and the tiny crustaceans they eat, then watch the capture under a dissecting microscope. Hydras, like jellyfish, have stinging cells in their tentacles.
> 
> "They usually reproduce by budding. If you cut them up in pieces, the odds are good that a piece will become a new hydra, sometimes a hydra with two heads.
> 
> ***
> 
> "Hydras are much simpler, made of just a few layers of cells. But they still respond to chemical signals sent out by genes as they grow into a tubelike body and tentacle-encircled maw.
> 
> "However, scientists in Israel, who cut up a lot of hydras in the process of their experiments, found that there are structures in even a small bit of hydra that also guide growth.
> 
> "A hydra body has a kind of scaffolding made of protein fibers that act like muscles and help the organism keep its shape. The way these actin fibers are arranged helps determine how the hydra grows, even in a hydra scrap.
> 
> ***
> 
> "this is not simply a matter of growing along the length of the fibers, because the first thing a bit of hydra does in regenerating a full animal is fold into a sphere. Somehow — and this is a subject for future research — the aligned fibers tell the growing ball of cells which direction to grow.
> 
> "Some scraps grow better than others. A ring cut horizontally through the body of the hydra often ends up with a confused alignment of the fibers when it folds into a ball. The result may be a hydra with two heads."
> 
> Comment: It is amazing what living organisms can do. If the Times website will allow it, look at the one minute video of regeneration. This is a very simple organisms, but some Earthworms can be cut in pieces and each with regenerate, and they are more complex with nerve networks. Lizards can drop tails and replace them.