210 



CILIATE FIBRILLAR SYSTEMS 



out its course. Both were surrounded by a delicate membrane, the 

 "Strangscheide," in the same manner that the whole St iel Strang is en- 

 closed within the outside membrane, "Stielscheide," of the stalk. 



The Stielmuskel, so most authors (e.g., Engelmann, 1875; Wrzesniow- 

 ski, 1877) agreed, was made up of distinct fibrils running variously 

 transverse or parallel to its long axis. For Biitschli (1889), however, 

 this composition of the Stielmuskel represented rather (and probably 

 more in line with his alveolar hypothesis ) an attenuated meshwork. And 

 Ehrenberg (1838), Leydig (1883), et al. could apparently see cross 

 striations in the Stielmuskel of some vorticellids, comparable with those 

 of metazoan muscle. 



Entz (1893) described for the giant stalk of Zoothamnium arhuscula, 



Figure 76. Spasmonem 

 (cross section) in Zoo- 

 thamnium. (Entz, 1893.) 



and as typical for all the Contractilia, a Stielstrang comprising three 

 well-defined fibers: a "Spasmonem," a "Splronem," and an "Axonem" 

 (Fig. 75), all enclosed within the Strangscheide. He identified the 

 Spasmonem with the Stielmuskel (noted above), and the Spironem and 

 Axonem with the Protoplasmastrang. 



In the smaller branches of Z. arbuscula, the Spasmonem (Stielmuskel) 

 is a round fiber which, in the main stalk, becomes compressed by the 

 adjacent Spironem so that a cross section of the former appears crescent- 

 shaped or, since one edge of the crescent is swollen, rather like the form 

 of a comma (Fig. 76). As shown by Engelmann (1875), it is bire- 

 fringent and may frequently be tinted a steel-gray or appear faintly 

 greenish or yellowish. It is stainable in carmine and disintegrates in 

 alkali and in mineral salts — reactions which are more rapid in the 

 younger stems, and which, according to Entz, would indicate that the 

 Spasmonem is not cellulose; neither is it chitin nor keratin, although 

 least unlike chitin. 



This age difference shows itself also in the finer structure of the 



