In Cyelidium, Pantotriehum, and Chat°. monas, and their loricated representatives, Cha. totypla, Chatoglenu, Peridiniton, and Gleno dinium, forming the families Cyclididw and Peridinaeadw, we first find a new system of locomotive organs making their appedrance in the shape of vibratile cilia.
The locomotive cilia are variously disposed in different genera ; sometimes they are disse minated over the entire surface of the animal, either irregularly or arranged in regular rows ; sometimes they are only partially distributed or are confined to the region of the mouth and anterior part of the body ; but, whatever their situation, their action is similar; they are inces santly in a state of active inotion, either pro pelling the animalcule through the water, or causing currents to flow in definite directions, by the agency of which food is brought to the oral opening. _ The geniis Stentor (fig. 8) contains some of the largest and most active animalcules be longing to the class, and, as might be expected, these are amongst the most conspicuous for the perfection of their locomotive organs. These beautiful creatures resemble gelatinous trum pets, the bodies of which are flexible and con tractile in all directions, either while swimming about freely in the water, or while attached, as they frequently are, to some foreign body by means of a little sucking disc which terminates the pointed extremity of the tail.
The whole of the trumpet-shaped body of Stentor is covered over with innumerable cilia, disposed in regular rows, and of sufficient size to be easily distinguishable by the microscope. Its broad end is terminated by a circular disc, the diameter of which is considerably larger than the widest part of the body. The entire surface of this disc is likewise covered with multitudes of cilia, arranged in regular con centric circles; and, moreover, its margin is fringed all around with a single row of cilia of larger dimensions, which by the rapid succes sion of their movements give the appearance of a wheel spinning rapidly round, and by its revolution causing powerful currents in the sur rounding water. At the lower part of the margin of the ciliated disc the ciliary zone turns inwards, forming a spiral fold around a funnel-like aperture (fig. 8) which leads to the mouth, and likewise lodges the orifice through which digested materials are cast out. The currents caused by the marginal fringe around the disc are all directed towards the oral aperture, and consequently, by bringing nutritive particles to the mouth, this part of the apparatus becomes eminently subservient to nutrition. In several species of Stentor, in addition to the apparatus of cilia described above, there is an additional riband-shaped band of these vibratile organs extending from near the mouth to a considerable distance tovvards the hinder part of the body, the outline of which has an undulated appearance.
The TrichodinT, or Urn animalcules, have no pedicle or elongated tail, but are provided with a fasciculus or circlet of cilia situated in front of their bodies, which are disc-shaped, bowl-shaped, or conical, the mouth being ap parently a single orifice situated in the ciliary circlet. One species of this group, T. pedicu lus, seems to be parasitically attached to the Hydra viridis, and allied forms have been met with in the respiratory laminre of several bi valve shell-fish, (Anodonta, Unto, &c.,) and also in Gyrodactylus coronatus, itself a parasite inhabiting the gills of the Crucian Carp (Cy prinus Carassius). That these animalcules are really Polygastrica, and not sterelminthous en tozoa, Ehrenberg satisfied himself by feeding them with indigo. Urocentrum seems to be similarly organized, only it is furnished pos teriorly with a sharp style-like process.
But perhaps the most remarkable as well as most elegant of all the forms of animalcules belonging to this group are the Vortieellte, (fig. 9,) the sight of which cannot fail to exact the untiring admiration of the microscopical observer. These beautiful little creatures might be compared to wine-glasses of microscopic ditnension, the bells of which are fixed to highly irritable stems, that are attached by their opposite extremity to some foreign body. These stems are endowed with the capability of extending themselves in the shape of straight filaments of exquisite tenuity, and on the slightest alarm or irritation, of shrinking into close spiral folds, so as to draw the little bell as far as possible from danger. The mouth of the bell is fringed with a circlet of cilia, which vibrate rapidly at the pleasure of the animal, causing a magnificent whirlpool in the sur rounding water, which brings nutritious sub stances that may be in the neighbourhood towards the oral orifice, the situation of which is nearly the same as in Stentor, above described, and thus the little being is abun dantly supplied with food. The true Vorti cellw, although generally found grouped toge ther in elegant bunches, always have single undivided stems; but in the genus Carchesium, the animals of which are similarly organised, the pedicles sprout from one another so as to have a branched or ramose appearance, while in the genus Episty/is, animals similar to Vor ticella and Carchesium are met with, the stems of which are quite stiff and inflexible, so much so indeed that the animalcules belonging to this group have obtained the name of " pil lar bells " ( Saulengliickchen).