=Shape and Structure.=--The paramecium’s whole body, like the ameba’s, is only one cell. It resembles a slipper in _shape_, but the pointed end is the hind end, the _front end_ being rounded (Fig. 14). The paramecium is propelled by the rapid beating of numerous fine, threadlike appendages on its surface, called _cilia_ (Latin, eyelashes) (Figs.). The cilia, like the pseudopods of the ameba, are merely prolongations of the cell protoplasm, but they are permanent. The separation between the outer _ectoplasm_ and the interior granular _endoplasm_ is more marked than in the ameba (Fig. 14). [Illustration: FIG. 14.--PARAMECIUM, showing cilia, _c_. Two contractile vacuoles, _cv_; the macronucleus, _mg_; two micronuclei, _mi_; the gullet (_Œ_), a food ball forming and ten food balls in their course from gullet to vent, _a_.] [Illustration: 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. [Illustration: 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. =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. 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. [Illustration: FIG. 17.--VORTICELLA (or bell animalcule), two extended, one withdrawn.] [Illustration: FIG. 18.--Euglena.] [Illustration: FIG. 19.--SHELL OF A RADIOLARIAN.]