nately elongating and rounding the foot. Can you discover other ways by which it moves? Does the hydra always stand upon its foot?
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Fig. 36.—Nettling Cell.
II. discharged, and I. not discharged.
Lasso Cells.—Upon the tentacles (Fig. 35) are numerous cells provided each with a thread-like process (Fig. 36) which lies coiled within the cell, but which may be thrown out upon a water flea, or other minute animal that comes in reach. The touch of the lasso paralyzes the prey (Fig. 37). These cells are variously called lasso cells, nettling cells, or thread cells. The thread is hollow and is pushed out by the pressure of liquid within. When the pressure is withdrawn the thread goes back as the finger of a glove may be turned back into the glove by turning the finger outside in. When a minute animal, or other particle of food comes in contact with a tentacle, how does the tentacle get the food to the mouth? By bending and bringing the end to the mouth, or by shortening and changing its form, or in both ways? (Fig. 34, C.) Do the neighboring tentacles seem to bend over to assist a tentacle in securing prey? (Fig. 34, C.)
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Fig. 37.—Hydra capturing a water flea.
Digestion.—The food particles break up before remaining
