THE INFUSORIA 203 



with loss of the posterior girdle of cilia, and elevation of the anterior 

 region bearing the adoral zone, which, as in the other groups of Ciliata, 

 is turned toward the left. The key to the other group of Peritrichida 

 is seen, Biitschli maintains, in the family Lichnophoridae, where the 

 individuals closely resemble hypotrichous forms (Fig. 114), being 

 oval, flattened ventrally, and arched dorsally. The cilia, as in the 

 Hypotrichida, are limited to the ventral surface, and an adoral zone 

 is present, which runs from the mouth near the middle of the left 

 body edge, entirely around the anterior region of the body, to form 

 an incomplete arc which terminates in the line of the mouth, but on 

 the right side. Another closed ring of cilia is present in the pos- 

 terior half of the ventral surface. The anterior and posterior rings 

 of cilia are separated in Lichnophora by a stretch of plasm in such a 

 way as quite to divide that surface into a posterior and an anterior 

 division (E). The posterior part becomes modified to form an 

 attaching organ upon which the animal creeps about upon its host ; 

 the anterior region at the same time is elevated, and held in a posi- 

 tion at right angles to the plane of attachment, the apparent stalk 

 which supports it being in reality the intermediate plasm between 

 the posterior and the anterior regions of the ventral surface (D). 

 Thus the curious anomaly arises of an animal whose anterior and 

 posterior ends represent parts of the same ventral surface. 



Biitschli derives the entire family of the Vorticellidae from this 

 primitive type, through forms like the Urceolarinae, where the 

 attaching disk, primarily, is not so far removed from the peristome, 

 nor so stalk-like, as it is in the present-day Lichnophoridae (D, E). 

 He argues that the Vorticella-ty^z is derived from the Urceolaria- 

 type by the attaching part of the ventral surface, i.e. the pos- 

 terior part being carried outward from the remainder of the ventral 

 surface, and thus borne upon a platform so that the two portions of 

 the same surface are no longer in the same plane (B). The anterior 

 ring of cilia is then supposed to have grown around the base of the 

 elevated portion until the original adoral zone of cilia now forms a ring 

 about the entire ventral surface. The new arm of this line of cilia 

 grows on past the mouth-opening and forms a spiral, which, looked 

 at from the ventral side, turns to the left, as in all other Ciliata seen 

 from the same surface. Looked at from the other side, however, i.e. 

 dorsally, the spiral turns to the right (C). This condition is practi- 

 cally represented by the genus Trichodina, which moves about on 

 the skin of various Invertebrata by means of the ciliated or attach- 

 ment disk, in reality the posterior part of the original primitive 

 ventral surface ; while the other portion is now carried dorsally and 

 parallel to the attachment disk, the mouth being on the left side of 

 this anterior part. In the Vorticellidae this posterior or attaching 



