coats. The outer coat is the ectoderm or "outer skin," the other is the endoderm or "inner skin" (Fig. 36). The cells in the outer skin of the green hydra contain those green grains or chlorophyll which give the green color. It is curious to see that the hydra makes its fingers, or tentacles, somewhat as the amoeba makes its feet, or pseudopodiæ (Fig. 36). It pushes out its two coats in the same way, but it never allows its fingers to swallow it as the amœba is swallowed by
Fig. 36.—Hydra pushing out its Fingers.
its feet. When it is disturbed or frightened, it seems to swallow its fingers, or rather puts them all into its mouth, like a sulky child. It is a good deal higher up in the world than the amœba, for you remember that had to eat with its feet. Then, too, the hydra has a more aristocratic walk than the amœba. You can see it plant its foot firmly against the glass, then proudly bow its back and draw the rest of its body up to the foot, in the form of a loop, like the "looping caterpillar" (Fig. 37).
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| Fig. 37.—Looping Caterpillar. | Fig. 38.—Thread-Cell. | Fig. 39.—Thread-Cell. |
To be sure, it goes backward, but it is a great improvement on the walk of the amœba. It is also an excellent swimmer. You may often see it lift up its foot and dash into the water in search of food. It is one of the funniest things in the world to see the hydra catch its prey. I remember in my old geography a picture of Indians catching wild-horses with lassos. The lasso is a long rope with a loop at the end,
