Antique engraved illustration of the hydra stinging fibre. Vintage illustration of the hydra stinging fibre. Old engraved picture. Longitudinal cross section of the hydra. Book illustration published 1907. Hydra has two main body layers, which makes it diploblastic . The layers are separated by mesoglea, a gel-like substance. The outer layer is the epidermis, and the inner layer is called the gastrodermis, because it lines the stomach. The cells making up these two body layers are relatively simple. Hydramacin is a bactericide recently discovered in Hydra it protects the outer layer against infection. A single Hydra is composed of 50,000 to 100,000 cells which consist of three specific stem cell populations that will create many different cell types. These stem cells will continually renew themselves in the body column. Hydras have two significant structures on their body: the head and the foot . When a Hydra is cut in half, each half will regenerate and form into a small Hydra the head will regenerate a foot and the foot will regenerate a head . If the Hydra is sliced into many segments then the middle slices will form both a head and a foot . Respiration and excretion occur by diffusion throughout the surface of the epidermis, while larger excreta are discharged through the mouth.

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拍攝者： Romannerud