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in a mass at the inner end of the gullet, become separated from it as a food ball (Fig. 14), and sink into the soft protoplasm of the body. The food balls follow a circular course through the endoplasm, keeping near the ectoplasm.

Reproduction.—This, as in the ameba, is by division, the constriction being in the middle, and part of the nucleus going to each half. Sometimes two individuals come together with their mouth-grooves touching and exchange parts of their nuclei (Fig. 16). They then separate and each divides to form two new individuals.

Fig. 17.—Vorticella (or bell animalcule), two extended, one withdrawn.

Fig. 18.—Euglena.

We thus see that the paramecium, though of only one cell, is a much more complex and advanced animal than the ameba. The tiny paddles, or cilia, the mouth-groove, etc., have their special duties similar to the specialized organs of the many-celled animals to be studied later.

Fig. 19.—Shell of a Radiolarian.

If time and circumstances allow a prolonged study, several additional facts may be observed by the pupil, e.g. Does the paramecium swim with the same end always foremost, and same side uppermost? Can it move backwards? Avoid obstacles? Change shape in a narrow passage? Does refuse