CILIATE FIBRILLAR SYSTEMS 217 



traction of the stalk is referable to contractile properties of some one 

 or more of its components. Dujardin (1841) was apparently the only 

 one to regard the stalk sheath as the seat of that contractility. Ehren- 

 berg's Stielniuskel was for him the contractile component, but also the 

 only component that he had recognized within the stalk sheath. Of the 

 three fibers into which this StieUnuskel was later analyzed, viz., the 

 Spasmonem and Spironem and Axoyieni, Kiihne (1859) considered 

 the latter two, or Protoplasmastrang, as the contractile organelle. This 

 he likened to the sarcoglia of metazoan muscle. Other proponents of 

 this contractile theory (Czermak, 1853; Engelmann, 1875; Wrzesniow- 

 ski, 1877; and others) regarded the Spasmonem as the contractile fiber 

 which, for later authors, represented a bundle of fibrils or myonemes 

 that continued without interruption into the body of the vorticellid. 



2. Apparently there is general agreement among all the investigators 

 that the mechanism of stalk extension inheres in the elastic properties 

 of the pellicle (Butschli, 1889; Entz, 1893). Only Kuhne (1859), who 

 alone regarded the Spironem and Axonem as the contractile organelles, 

 attributed elasticity to both the pellicle and the Spasmonem, thus to 

 account for the stalk's extension. 



3. While the majority, as noted, support the contractile theory of 

 stalk contraction, there is a minority group who maintained that the 

 vorticellid stalk, in its quick spiraling retraction, actually does not con- 

 tract as such but instead recoils somewhat as a coiled spring. 



A chief proponent of this elastic theory is Entz (1893), who sees the 

 Spasmonetn not as a contractile fiber but, like Kiihne, as an elastic fiber. 

 This organelle is, according to Entz, primarily responsible for the sudden 

 recoil of an extended stalk. He likens this elastic fiber to a curly hair 

 which when stretched and then released will resume its spiral form. 



The opposing force, tending to "stretch" this normally spiral Spas- 

 monem, is inherent in the elastic pellicle. Thus pellicle and Spasmonem 

 constitute a pair of "antagonistic elements." 



Associated with this pair is another pair of antagonistic elements, 

 viz., (1) the longitudinal myonemes in (a) the stalk sheath and (b) 

 the Spironem; and (2) the circular myoneme in (a) the stalk sheath 

 and (b) the Spironem. These opposing pairs of fibrils are relatively 

 weak, but of a strength sufficient to determine by their antagonistic 

 contractions whether the stalk "contracts" with the recoil of the elastic 



