6 ELECTRO-PHYSIOLOGY CHAP. 



with a contractile stalk the fibrils do not end here, but unite to 

 form a thread-like organ, which enters the stalk, and usually runs 

 right along it. This filament or muscle, almost without exception, 

 runs down inside the sheath of the stalk in a sharp spiral. The 

 sheath is a cylindrical tube of medium diameter, which attaches 

 itself at the distal end to some foreign body. It has a slender, 

 elastic wall of chitinous composition. The interior of the seem- 

 ingly hollow stalk is filled with a homogeneous, vitreous, trans- 

 parent mass of apparently gelatinous consistency. In Vorticella 

 and Carchesium the filaments run through the stalk in a very 

 elongated spiral, the number of turns varying with the length of 

 the pedicle. According to Czermak (5) they may range from 

 to 12. In very short -stalked Vorticellte there may be only 

 11 turn. In Zoothamnium the muscle - filaments do not run 

 peripherally along the sheath of the stalk as in Vorticella and 

 Carchesium, but lie close to the axis, surrounded on all sides by 

 the homogeneous medullary substance, with no distinct spiral. 



Since the filament is formed by the junction of the body- 

 myonema, we may presume that it will have a fibrillated struc- 

 ture. In most forms the fibrils appear to lose their identity in 

 the filament, and run together in a homogeneous mass. Yet this 

 can be in appearance only, since the thick muscle - threads of 

 certain Zoothamnia are distinctly fibrillated. This point will in 

 all probability be established generally, by methods similar to 

 those which Ballowitz employed to discover the fibrillated struc- 

 ture of the nagellum of the sperniato-somata. 



The contraction phenomena in the stalk of Vorticella appear 

 to be normally sharp and sudden (" convulsive "). The contrac- 

 tion usually affects the whole stalk, which shrinks into a low and 

 narrow-pitched spiral (helicoid), the turns being in close juxta- 

 position. The body of the animal usually contracts simultane- 

 ously with the pedicle. At times the stalk is only partially 

 contracted, and both the upper and lower halves seem able to shrink 

 locally, without implicating the remainder (Czermak, Klihue). The 

 unrolling of a contracted stalk is a much slower process ; it also 

 may vary in direction, beginning, i.e., from above or below, and 

 sometimes remaining incomplete for a long period. 



Czermak (Z.c.) was the first to show that only the jUmiinits of 

 the stalk, in accordance with the function of the fibrils of the 

 body-plasma, are the seat of contractility ; it had previously been 



