The Ciliata are almost all free-swimming animals with the exception of most of the Peritrichaceae, and of the genera we now cite. _Folliculina_ forms a sessile tube open at either end; and _Schizotricha socialis_ inhabits the open mouths of a branching gelatinous tubular stem, obviously secreted by the hinder end of the animal, and forking at each fission to receive the produce. A similar habit to the latter characterises _Maryna socialis_; all three species are marine, and were described by Gruber.[168] _Stentor_ habitually attaches itself by processes recalling pseudopodia, and often forms a gelatinous sheath. The majority of the Oligotrichaceous Tintinnidae inhabit free chitinous tests often beautifully fenestrated, as in _Dictyocystis_. Many genera are parasitic in the alimentary canal of various Metazoa, but none appear to be seriously harmful except _Ichthyophtheirius_, which causes an epidemic in fresh-water fish. Quite a peculiar fauna inhabit the paunch of Ruminants. _Nyctotherus_ and _Balantidium_ are occasionally found in the alimentary canal of Man.[169] The Gymnostomaceae are predaceous, feeding for the most part on smaller Ciliates. We have described the peculiar character of the mouth and pharynx in this group, and the mail-like pellicle of _Coleps_ (Fig. 54). _Loxophyllum_ is remarkable for the absence of cilia from one of the sides of its flattened body, and the tufts of trichocysts studding its dorsal edge at regular intervals. _Actinobolus_ has numerous tentacles, exsertile and retractile, each bearing a terminal tuft of trichocysts, which serve to paralyse such active prey as _Halteria_. _Ileonema_ has one tentacle overhanging the mouth; and _Mesodinium_ has four short sucker-like projections around it.[170] It has only two girdles {153}of cilia, which are stout and resemble fine-pointed cirrhi. In _Dysteria_ the cilia are exclusively ventral, and the naked dorsal surface has its pellicle condensed into a bivalve shell; a posterior motile process ("foot") and a complex pharyngeal armature add to the exceptional characters of the genus. The Aspirotrichaceae are well known to every student of "Elementary Biology" by the "type" _Paramecium_ (Fig. 55), so common in infusions, especially when containing a little animal matter. _P. bursaria_ often contains in its endosarc the green symbiotic Flagellate _Zoochlorella_. _Colpoda cucullus_, very frequent in vegetable infusions, usually only divides during encystment, and forms a brood of four. _Pleuronema chrysalis_ (Fig. 57) is remarkable for its habit of lying for long periods on its side and for its immense undulating membrane, forming a lip on the left of its mouth; _Glaucoma_ has two, right and left.