524 DESCEiPTioK OF {^Polygastrtcct, 



genus by the surface of the body being destitute of cilia ; they pos- 

 sess a vibrating fasciculus or wreath of cilia anteriorly ; the oral 

 opening is simple, and not spiral. They are mostly disc-shaped or 

 conical. Three species have a wreath of cilia around the anterior 

 pai-t, and on one side of its margin is a simple oral opening. T. pedi- 

 cuius has the posterior end abruptly truncated, like the front, and also 

 surrounded with a wreath of curved setae, which it employs as feet. 

 In T. tentaculata there is a kind of jji'oboscis. The polygastric stnicture 

 can be demostrated in T. pediculus and T. grandinella, by coloured 

 food ; in the other species it may be observed without artificial aid. 

 In all, the ova are clear and limpid as water. A kidney-shaped 

 gland is seen in T, pediculus. 



This geniis, TricJiodina, agrees ia the main with that of Urceolaria 

 (Duj . ) ; but also includes " some Keronia {HaUeria) with several doubt- 

 ful Infusoria." — Dujardin, however, defines his Urceolaria as having 

 the wreath of cilia extended spirally to reach the mouth ; whilst in 

 his Trichodma, that the oral opening is not spiral. 



Many species live parasitic on fresh-water Mollusca, or Zoophytes ; 

 but others have been found in sea-water. 



Trichodina tentaculata. — Body discoid, as shewn at P. 4, f. 227; 

 it is destitute of the wreath of cilia, but it has a fasciculus of 

 vibratile cilia, and a styliform proboscis, as seen in the engraving. 

 Size l-280th. 



T. Pediculus {Cyclidium pediculus, M.) = Urceolaria SteUina, (Dnj.) 

 — Body depressed, of an urceolate and discoid shape, as shewn at 

 figs. 228, 229, and 230 ; with a wreath of vibratile cilia anteriorly, and 

 anotlier of shoii; moveable uncinate cilia, or hooked seta?, posteriorly. 

 Ehrenberg remarks, "I have fed this species many times with 

 indigo, and have seen numerous stomachs fiUed with the blue matter ; 

 it always runs upon the back, where there is a wreath of twenty - 

 four to twenty-eight mobile hooks (or uncinate cUia), and has the 

 mouth and vibrating wreath of forty-eight to sixty-four cilia directed 

 upwards." It appears to feed upon the little granules of the body 

 of the fresh-water Polypi {Hydra) drawn in Plate 7, of the Micros- 

 copic Cahinet. Figs. 228 and 229 arc side views, attached to a portion 

 of a polype; fig. 230 is a top view. Size 1-5 70th to l-280th. 



