Left: Vorticella, with posterior circlet of cilia in process of separation—Stein.
Right: Vorticella in process of self-division. A new frontal wreath in formation in each of the semi-lunar spaces.
Different specimens and species of Vorticellæ vary in the length of their bells from one three or four thousandth to one hundred and twentieth of an inch, and when they are tolerably large, the dark ground illumination produces a beautiful effect. The bells shine with a pearly iridescent lustre, and their cilia flash with brilliant prismatic colours.
Left: Vorticella microstoma, showing alimentary tube, ciliated mouth, and formation of a gemma at the base, 300 linear.—Stein.
Right: Vorticella microstoma, the encysted animal protruding through a supposed rupture of the tunic.
The Vorticellina belong to the upper division of the Protozoa—the ciliata, or ciliated animalcules, and they have a mouth, an œsophagus, and an orifice for the exit of their food.
Many observers used to ascribe to those creatures a complete intestinal canal, but such an apparatus is now believed not to exist in any of the Infusoria. Food particles, after leaving the œsophagus, are thrust forward into the sarcode, or soft flesh, and any cavity thus formed acts as a stomach.
The bells or cups are not, as might be fancied from a casual inspection, open like wineglasses at the top, but furnished with a retractile disk or cover, on which the cilia are arranged. Their stalks are not simple stems, but are hollow tubes, which in the genus Vorticella are furnished with a muscular band, by whose agency the movements are principally made.
Some of the Vorticellids will be observed to leave their stalks, having developed cilia round their base, and may be seen to swim about in the enjoyment of individual life. They are also capable of becoming encysted, that is, of secreting a gelatinous cover.
