CILIATA 141 



find in the Protista, and we can speak without exaggeration of 

 the " organs " formed thereby. 



The form of the body, determined by the firm pellicle or 

 plasmic membrane, is fairly constant for eaeli species, ihougli 

 it may be subject to temporary flexures and contractions. T'lu- 

 pellicle varies in rigidity ; where the cilia are abundant it is pro- 

 portionately delicate, and scarcely differs from the ectoplasm proper, 

 saye for not being alveolate. In the Peritrichaceae it is especially 

 resistant and proof against decay. In Coleps (Gymnostomaceae) it 

 is hardened and sculptured into the semblance of plate-armour, and 

 the prominent points of the plates around the mouth serve as teeth 

 to lacerate other active Protista, its prey ; but, like the rest of 

 the protoplasm, this disappears by decay soon after the death of 

 the Coleps. Where, as in certain Oligotrichaceae, cilia are absent 

 over part of the body, the pellicle is hardened ; and on the dorsal 

 face and sides of Dysteria it even assumes the character of a 

 bivalve shell, and forms a tooth-like armature about the mouth. 



From the pellicle protrude the cilia, each of which is con- 

 tinued inwards by a slender basal filament to end in a " basal 

 granule " or " blepharoplast." The body-cilia are fine, and often 

 reversible in action, which is exceptional in the organic world. 

 They may be modified or combined in various w^ays. We have 

 seen that in Stylonychia some are motionless sensory hairs. The 

 cirrhi and setae sometimes fray out during life, and often after 

 death, into a brush at the tip, and have a number of blepharo- 

 plasts at their base. The same holds good for the membranellae 

 and undulating membranes. They are thus comparable to tlie 

 " vibratile styles" of Eotifers (Vol. II. p. 202) and the "combs" 

 or " Ctenophoral plates" of the Ctenophora (p. 412 f.).^ 



The ectosarc has a very complex structure. Like other 



^ Tail-like appendages are found in Scaphiodon and in Dysteria and its allies 

 (Gymnostomaceae), Urocentrum (Aspirotrichaceae), Discomoiyha and Caenomorpha 

 (Heterotrichaceae). In the first two and last two cases they are prolongations of 

 the body ; in tlie third an aggregate of cilia. One or more long caudal setiforni 

 cilia are present in the genera Lembadion, Pleuroncma, Cyclidium, Lemhus, 

 Cinctochilum, Ancistrum, and Uronema ; all these are addicted to making spring- 

 ing darts. Tufts of cilia of exceptional character often serve for temporary attach- 

 ment. The stalk (or at least its external tube) of the Peritrichaceae appears to be 

 the chitinous excretion of a zone of such cilia. Faure-Fremiet terms such a zone 

 or annular brush a "scopula" ("Struct, de I'app. fixateur chez les Vorticellides," 

 Arch. ProHst. vi. 1905, p. 207). For a discussion of the finer structure of the cili.i 

 in Ciliata, and the mechanism of their action, sec Schuberg, Arch. Prvtisl. vi. 

 1905, p. 61. 



