[Illustration: Vorticella microstoma, showing alimentary tube, ciliated mouth, and formation of a gemma at the base, 300 linear.--_Stein._] [Illustration: 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 oesophagus, 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 oesophagus, 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. [Illustration: Encysted Vorticella, showing the obliteration of special organs by the advancement of the process.--_Pritchard._] These changes are exhibited in the annexed cuts, which are copied from known authorities. By careful observation of the bodies of Vorticellids, a contractile vesicle may be observed, which appears to cause a movement of fluids, that is probably connected either with respiration or secretion. Another piece of apparatus in this family, but not confined to it, is the so-called _nucleus_, which in this case is of a horseshoe shape and granular texture, and greater solidity than the surrounding parts. The functions of this organ formed the subject of various conjectures, but it is now generally held to be an ovary. [Illustration: Vorticella microstoma, in process of encystment, 300 linear; in the last the inclosing tunic is plainly developed.--_Stein._]