Fig. 15.
Nucleus and Vacuoles.—There is a large nucleus called the macronucleus, and beside it a smaller one called the micronucleus. They are hard to see. About one third of the way from each end is a clear, pulsating space (bb. Fig. [15]) called the pulsating vacuole. These spaces contract until they disappear, and then reappear, gradually expanding. Tubes lead from the vacuoles which probably serve to keep the contents of the cell in circulation.
Fig. 16.—Two Paramecia exchanging parts of their nuclei.
Feeding.—A depression, or groove, is seen on one side; this serves as a mouth (Figs.). A tube which serves as a gullet leads from the mouth-groove to the interior of the cell. The mouth-groove is lined with cilia which sweep food particles inward. The particles accumulate 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.
Fig. 17.—Vorticella (or bell animalcule), two extended, one withdrawn.
Reproduction.—This, as in the amœba, 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.
