Although ectoderm and endoderm layers may appear superficially similar, and both consist mostly of the same two types of cells, slender sensory cells and columnar epithelial cells with muscle fibrils in their bases, it has been shown that during development they have undergone a basic differentiation which cannot be reversed merely by changing their position in the hydra. In one experiment about sixty hydras were turned inside out (by manipulation with needles). About a third of the hydras did not adjust but underwent a period of "depression" followed by death. About a third were able to return themselves right side out. And about a third of the hydras remained turned but readjusted themselves by a migration of the cells of the ectoderm and endoderm past each other in opposite directions through the jelly-like material between. In one hydra the cells had migrated and taken up their normal positions within two hours after the hydra had been turned inside out. Such reorganized hydras ingested food two days after the time of turning.
More importantly, if a planarian knew the location of a bomb, would you be required to cut off its head and feed it to another, friendly planarian? To stop terror? I mean, the first one would grow its head back later, so, no biggie.
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