. Principes de la biologie moderne. La biologie. 196 - La cellule F. Â ¢ ***&gt ;..Â", Â Â ¢* **, fig. 11-5. Un Vorticella, élargi l'état. Remarque Le myoneme que s'étend le long de la tige. (Bausch et Lomb Optical Co., Inc.) Les particules étrangères sont effectuées à partir de la les rois jusqu'à la trachée dans la gorge. Dans les protozoaires, toutefois, la direction de l'battement ciliaire peut être inversée temporairement, comme lorsqu'une paramécie recule d'un obstacle. Un flagelle active affiche une MYONEME .tourbillonnant Fig. 11-6. Voriicella pétiolées, un protozoaire cilié ; A, B ; élargi, contracté. La contraction s'effectue

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. Principles of modern biology. Biology. 196 - The Cell F. ⢠***>..», â **â¢*, Fig. 11-5. A living Vorticella, expanded condition. Note the myoneme that extends along the stalk. (Bausch and Lomb Optical Co., Inc.) foreign particles are carried from the kings up through the trachea into the throat. In the Protozoa, however, the direction of the ciliary beat may be reversed temporarily, as when a paramecium backs away from an obstacle. An active flagellum displays a whirling .MYONEME Fig. 11-6. Voriicella, a stalked ciliated protozoan; A, expanded; B, contracted. The contraction is effected by the shortening of the myoneme. (Other intracellular structuresânucleus, vacuole, etc.âare omitted from the figure.) movement, especially at the free end, like the twilling of a whip. In some cases this action pulls the cell forward, as a propeller pulls an airplane, but in others it pushes the cell as a propeller pushes a steamship. Recent electron microscope studies, ini- tiated by Keith Porter of the Rockefeller Institute for Medical Research, show that the cilia and flagella from a wide variety of plants and animals display a uniform struc- ture of considerable complexity. Always there seem to be ten pairs of fibrillae that extend lengthwise out into the cilium (or flagellum). The arrangement of these ten double fila- ments always conforms to a similar pattern, which is best shown in cross-sectional view (Fig. 11-8). Probably, these ciliary fibrillae are comparable to myofibrillae (p. 435), the contractile elements of muscle fibers, but ex- perimental evidence is not available. Amoeboid Movement. The amoeba moves by means of pseudopodia, which are strictly temporary protoplasmic extensions, projected from the surface of the cell. During locomo- tion, the protoplasm of the amoeba continues to flow forth into the leading pseudopodium, so that the cell moves as the pseudopodium extends. The pseudopodia also play a part in ingestion, when the amoeba engulfs small fo

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