138 PROTOZOA 



Stylonychia, Elirb. ; Kerona, 0. F. Miill. ; Oxytricha, 

 Ehrb. ; Euplotes, Ehrb. ; Stichotricha, Perty ; Schizo- 

 tricha, Gruber. 

 (iv.) Body cilia reduced to a posterior- girdle, or temporarily 

 or permanently absent ; peristome anterior, nearly 

 circular, edged by the adoral wreath,! bounded by a 

 gutter edged by an elevated rim or collar. 



Order 6. Periteichaceab. 



Lichnophora, CI. ; Trichodina, Ehrb. ; Vorticella, L. ; 

 Zoothamnium, Bory ; Garchesium, Ehrb. ; Epistylis, 

 Ehrb.; Opercularia, Lamk.; Vaginicola, Lamk. ; 

 Pyxicola, Kent ; Gothurnia, Ehrb. ; Scyphidia, 

 Laohmann ; Ophrydium, Bory ; Spirochona, St. 



The Ciliata have so complex an organisation that, as with the 

 Metazoa, it is well to begin with the description of a definite type. 

 .For this purpose we select Stylonychia mytilus, Ehrb. (Fig. 49), 

 a species common in water rich in organic matter, and relatively 

 large (1/75" = ;^ mm.). It is broadly oval in outline, with the 

 wide end anterior, truncate, and sloping to the left side behind ; 

 the back is convex, thinning greatly in front ; the belly flat. 

 It moves through the water either by continuous swimming or 

 by jerks, and can either crawl steadily over the surface of a solid 

 or an air surface such as an air bubble, or advance by springs, 

 which recall those of a hunting spider. The boundary is every- 

 where a thin plasmic pellicle, very tender, and readily undergoing 

 diffluence like the rest of the cell. From the pellicle pass the 

 cilia, which are organically connected with it, though they may 

 be traced a little deeper ; they are arranged in slanting longitu- 

 dinal rows, and are much and variously modified, according to 

 their place and function. On the edge of the dorsal surface they 

 are fine and motionless, probably only sensory (s.A.) ; except three, 

 which protrude well over the hinder end (c.jj.), stout, pointed, and 

 frayed out at the ends, and possibly serving .as oars or rudders 

 for the darting movements. These are distinguished from simple 

 cilia as " cirrhi." 



At the right hand of the frontal area there begins, just within 

 the dorsal edge, a row of strong cilium-like organs (Fig. 49, per) ; 

 these, on careful examination, prove to be transverse triangular 

 plates, which after death may fray into cilia.^ They are the 



' Dextrorse in all but Lichnophora and Spirochona. 



^ Each membranella is a transversely elongated oval in reality, and below it is 

 a double row of basal granules, corresponding to the individual cilia that consti- 

 tute it. Similarly, the undulating membranes have a single row of basal granules. 



