VORTICELLA, vor-tT-slia, type of a family (Vorticellidce) of attached or free forms of peritrichous ciliates (animalculw), in which the adoral zone of cilia, where seen from above, forms a right spiral (dexiotropic), while a sec ondary circlet of cilia near the aboral end may be either permanent or transient.. The true vor ticellids, represented well by the common bell animalcule, are without a permanent second cir cle of cilia, and the penstome may be coin pletely included within a peristome fold which contracts sphincter-like about it. The steni either firm and constant in length, or flexible and capable of being contracted suddenly when it becomes a short close spiral. The individuals also are motnited on a single unbranched stalk or grouped on a common branching stalk in colonial existence. The simplest type of repro duction is longitudinal division, winch may re sult in producing two individuals in a branched stalk, or one of the two may become detached and, propelled by a newly-formed circle of cilia near the basal end, lead a free existence for a time. Soon the free form settles down and de
velops a stalk. Conjugation has been observed and always talces place between a stalked form and a free-swimming form produced by bud ding. The bell-animalcule has long been a fa vonte object of microscopical study from its abundance and easily observed structure and ac tivities. Ehrenberg (1838) made an extensive study of these organisms, and maintained that they possessed the complete organ systems of higher forms. The demonstration of their uni cellular nature necessitated the abandonment of this view. The group is rich in number and va riety of species. They are found in all sorts of aquatic environments but are exceptionally abun dant in some types of polluted streams.