Fig. 59.—Stentor polymorphus. I, Young individual attached, extended; II, adult in fission, contracted; cv in I, afferent canal of contractile vacuole; in II, contractile vacuole; N, moniliform meganucleus (micronuclei omitted); o, mouth; the fine lines are the myoneme fibrils. (From Verworn.)
Among Peritrichaceae, Vorticella (Fig. 60) and its allies have long been known as Bell-animalcules to every student of pond-life. The body has indeed the form of an inverted bell, closed at its mouth by the "peristome," or oral disc; this is a short, inverted truncate cone set obliquely so that its wide base hardly projects at one side, but is tilted high on the other; the edge of the bell is turned out into a rim or "collar," separated from the disc by a deep gutter. The collar, habitually everted, or even turned down, contracts over the retracted disc when the animal is retracted (E2), which is brought about by any sort of shock, or when it swims freely backwards. For the latter purpose a posterior ring of cilia (or rather membranellae) is developed round the hinder end of the bell (A, cr, E3). The cilia of the adoral wreath are very strong, united at the base into a continuous membrane, and indeed themselves partake of the composite nature of membranellae. The wreath forms more than one turn of a right-handed spiral, the innermost turn ending abruptly on the disc, the outer leading down into the mouth at the point where the disc is most tilted and the groove deepest.[[174]] The pharynx (p) is long, and contains an undulating membrane (u.m) on its inner side projecting out through the mouth, and numerous cilia; it leads deep into the body (p). The first part is distinguished as the "vestibule" (v), as into it opens the anus, and the contractile vacuole (c.v.), the latter sometimes opening by a reservoir (r). The body contains in the ectoplasm myonema-fibrils which, by their contraction, withdraw the disc, and at the same time circular fibrils close the peristome over it. In the type-genus the pellicle is continued into a long, slender elastic stalk (s), of which the longitudinal myoneme fibrils of the ectoplasm converge to the stalk, and are prolonged into it as a spirally winding fibre, sometimes transversely striated.[[175]] The effect of the contraction of this is to pull the stalk into a helicoid spiral (like a coil-spring), with the line of insertion of the muscle along the inner side of the coils, which is, of course, the shortest path from one end to the other (Fig. 60, B).
Fig. 60.—Vorticella. A, expanded; B, stalk in contraction; c, eversible collar below peristome; cr, line of posterior ciliary ring; c.v, contractile vacuole; m, muscle of stalk; N, meganucleus; n, micronucleus; p, pharynx; r, reservoir of contractile vacuole; s, tubular stalk; u.m, undulating membrane in vestibule; v, hinder end of vestibule. E1, E2, two stages in binary fission; E3, free zooid, with posterior wreath; F1, F2 division into mega- and micro-zooids (m); G1, G2, conjugation; m, microzooid. (Modified from Bütschli, from Parker and Haswell.)
The members of the Vorticellidae are very commonly attached to weeds or to various aquatic Metazoa, each species being more or less restricted in its haunts. Vorticella, the type, is singly attached to a contractile stalk; fission takes place in the vertical plane, and one of the two so formed retains the original stalk, while the other swims off (Fig. 60, E1-E3), often to settle close by, so that the individuals are found in large social aggregates, side by side, fringing water-weeds with a halo visible to the naked eye, which disappears on agitation by the sudden contraction of all the stalks. Carchesium and Zoothamnium differ from Vorticella in the fact that the one daughter-cell remains attached by a stalk coming off a little below the body of the other, so as to give rise to large branching colonies.
In Carchesium (Fig. 51) the muscular threads of each cell are separate, while in Zoothamnium they are continuous throughout the colony. Epistylis has a solid, rigid stalk, and may give rise to branching colonies, which often infest the body of the Water-Fleas (Copepoda) of the genus Cyclops. Opercularia is characterised by the depth of the gutter, the height of the collar, and the tapering downward of the elongated disc. Vaginicola, Pyxicola, Cothurnia, Scyphidia, all inhabit tubes, some of extreme elegance. Ophrydium is a colonial form, found in ponds and ditches, resembling Opercularia, but inhabiting tubes of jelly[[176]] that coalesce by their outer walls into a large floating sphere; it usually contains the green symbiotic Flagellate Zoochlorella. Trichodina is free, short, and cylindrical, with both wreaths permanently exposed, and is provided with a circlet of hooks within the aboral wreath. It is often parasitic, or perhaps rather epizoic, on the surface of Hydra (see p. [254]), gliding over its body[[177]] with a graceful waltzing movement; it occurs also in the bladder and genito-urinary passages of Newts, and even in their body-cavity and kidneys.
II. Suctoria = Tentaculifera
Infusoria with cilia only in the young state,[[178]] without mouth or anus, but absorbing food (usually living Ciliates) by one or more tentacles, perforated at the apex; mostly attached, frequently epizoic, rarely parasitic in the interior of other Protozoa.
Acineta, Ehrb. (Fig. 61, 2); Amoebophrya, Koppen; Choanophrya, Hartog (Fig. 62); Dendrocometes, St. (Fig. 61, 4); Dendrosoma, Ehrb. (Fig. 61, 9); Endosphaera, Engelm.; Ephelota, Str. Wright (Fig. 61, 5, 8); Hypocoma, Gruber; Ophryodendron, Cl. and L. (Fig. 61, 7); Podophrya, Ehrb. (Fig. 61, 1); Rhyncheta, Zenker (Fig. 61, 3); Sphaerophrya, Cl. and L. (Fig. 61, 6), Suctorella, Frenzel; Tokophrya, Bütschli.