Kerónia.—In this family the body is soft, irregularly ciliated, without a special integument, but has an oblique row of vibratile cilia leading to the mouth, and stouter cilia or bristles (setæ) on certain parts of the body. The sacculi often contain Diatomaceæ, &c.
Oxyt´richa gib´ba ([Pl. XI.] fig. 27) has a colourless, oblong body, somewhat expanded in the middle, with setæ at the two ends. In the side view (fig. 27 a), the body is seen to be convex above and flattened beneath.
Paramec´ina.—The species belonging to this family have a soft, flexible body, which is usually oblong and flattened beneath, with an integument covered regularly with pits and rows of cilia.
Col´poda cucul´lus ([Pl. XI.] fig. 30) has a slightly compressed body, ciliated all over, and kidney-shaped or rounded on one side and notched on the other, the surface exhibiting rows of nodules. The mouth is situated at the bottom of the notch.
Paramécium aurélia (fig. 28) has the body oblong or oblong-ovate, the mouth being placed near the anterior third of its under part. This infusorium is of comparatively large size, and is often found in immense numbers in infusions, which it renders milky. It is admirably adapted for showing the sacculi, which are easily filled with indigo. The body exhibits two remarkable stellate organs, consisting of a central contractile vesicle, surrounded by several radiately placed oval vesicles, which may be seen to contract and dilate with great regularity. The body is coated with very fine cilia.
Amphilep´tus fascíola (fig. 29) is furnished with an elongate fusiform or lanceolate flattened body, with a lateral oblique mouth.
Chil´odon cucul´lulus (fig. 37) has an oblong thin body, irregularly wavy on the sides; the mouth being situated obliquely in front of the middle, and furnished with a cylinder of parallel rod-like teeth.
Nas´sula el´egans (fig. 31) has the body ovoid or oblong, becoming globular when contracted, the mouth being furnished with teeth as in Chilodon. It is often found among Oscillatoriæ.
Urceolarína.—Vorticel´la convallária ([Pl. XI.] fig. 34) is very commonly met with in decomposing infusions. The bell-shaped body is fixed at the end of a slender stalk, which is often seen to be extended and then suddenly contracted into a spiral (fig. 34 a). The cilia are arranged around a raised rim at the front of the body, and extend down a fissure leading to the mouth. The sacculi of this infusorium may be readily filled with indigo. The process of longitudinal division may also often be observed, taking about an hour for its completion; and when the new individual is about to separate from the parent, a ring of cilia may be noticed to have sprung up around the base (fig. 36). The encysting process is also often visible, the cilia disappearing, and the body becoming globular and secreting a cyst around it; after a time the contents become resolved into a number of embryos, which escape by the bursting of the cyst (fig. 35). In some cases the Vorticella assumes the form of a Podoph´rya (fig. 40), the surface becoming covered with tentacle-like processes. This Podophrya was formerly considered a distinct species.
Vaginic´ola crystal´lina (fig. 33) is contained in a crystalline tube, from which the body can be protruded. The body is of variable form, presenting when fully extended a trumpet shape. The cilia exist at the anterior end, and extend down a lateral fissure as in Vorticella. It is found attached to Confervæ in the water of ponds and bog-pools.