MANUAL OF THE INFUSORIA. 



CHAPTER VIII. 



SYSTEMATIC DESCRIPTION OF THE INFUSORIA-CILIATA. 



Class IL CILfATA. 



ANIMALCULES partly or more or less completely clothed with vibratile 

 cilia, which constitute the essential organs of locomotion and prehension ; 

 no supplementary lash-like appendages or flagella ; certain of the cilia 

 often modified in the form of setae, styles, or uncini ; occasionally pos- 

 sessing more or less distinct membraniform expansions ; a well-developed 

 oral and anal aperture mostly present. 



With the class Ciliata we arrive at a group of the Infusoria with which micro- 

 scopists will feel comparatively at home, all its members being of relatively large 

 size, and for the most part very giants when set side by side with their flagelliferous 

 compeers described in the preceding volume. That no hard and fast line separates 

 the two groups from each other is nevertheless clearly illustrated by the series of 

 forms last described under the title of the Cilio-Flagellata, in many of which it 

 requires but the suppression of either the flagelliferous or ciliary appendages to con- 

 vert them into ordinary representatives of one or the other of the two leading ciliate 

 or flagellate infusorial classes. That the first-named group has been phylogenetically 

 derived from the Flagellata is by this annectant order fully demonstrated, its existence 

 at the same time assisting substantially in the establishment of an unbroken line 

 of increasingly complex Protozoic organisms, from the simplest Rhizopoda up to 

 the highest Ciliata. The probable lines of evolution by which these latter have 

 passed onwards into the Metazoic animal series will be presently discussed. 



Among the numerous indications of augmented complexity manifested among 

 the members of the class now about to be introduced, the following may be 

 mentioned : The cuticular or cortical element in the majority, if not all instances, 

 exhibits a much more complex composition. In by far the larger number of 

 instances it is delicately striate in a longitudinal direction, such striations conforming 

 with a distinct subdivision of its substance in the direction indicated into delicate, 

 highly elastic fibrillas, whose properties and function are closely akin to that of the 

 muscular tissue of the Metazoa, and has in consequence received the suggestive 

 name of the myophan layer. The oral aperture, or cytostome, with the Ciliata is, 

 excepting in the case of the endoparasitic Opalinidse, always more or less con- 

 spicuously developed, and is frequently supplemented by a complex horny buccal 

 apparatus, e. g. Prorodontidae, Dysteriidae, or it may be by an evertile proboscis, as in 

 Didinium. A modification in the first-named direction has been already notified in the 

 preceding volume in connection with the flagellate genera Astasia and Anisonema. 

 An anal passage or cytopyge, rarely recognizable in the Flagellata, is of almost uni- 

 versal recurrence among the Ciliata, being sometimes, as in Nyctotherus, so extensively 

 prolonged as, in conjunction with the oral aperture and pharyngeal tube, to constitute 



VOL. II. B 



