THE INFUSORIA 



179 



disk where their course is radial. The largest and most important of 

 all @f the myonemes are those forming the fourth set. These are 

 longitudinal muscle-fibres of considerable thickness running from the 

 centre of the disk radially toward the periphery, then continuing 

 down the sides of the bell as far as the ciliary girdle ( Wimperring\ 

 where they leave the wall of the body and come together to form the 

 thick muscle-strand of the stalk. The latter highly contractile organ 

 consists of a wall and of the central, contractile strands which are 

 bathed with a fluid contained within the walls of the stalk. The wall 

 itself, according to Entz, but contrary to Biitschli, is a continuation of 

 the living wall of the bell, in which membrane and underlying mus- 



Fig. 96. Zoothamnium arbuscula Ehr. [ENTZ.] 



A, Lower portion of main trunk. B. One of the branches of the main trunk, a, axoneme ; 

 p, spasmoneme ; s, spironeme. 



cular structures can be distinguished, as in the main portion of the 

 body. Biitschli, on a less substantial basis, described the stalk as a 

 secretion similar to the stalks of the Mastigophora and Sarcodina, and 

 chitinous in composition. The main strand within the stalk is formed 

 by the collection of the strands of the inner longitudinal myonemes, 

 and is covered by a delicate sheath which separates it from the fluid 

 or gelatinous matter surrounding it. Biitschli regards this sheath as 

 a continuous coat from the alveolar layer of the bell. The strand has 

 three threads which Entz calls spasmoneme, spironeme, and axoneme 

 (Fig. 96). The fibres of the first run to the base of the stalk. The 

 other two are closely connected, and both are made up of microsomes, 

 which Entz described as nucleus-like granules (karyophans} surrounded 

 by an ovoid matrix (cytophan\ These granules, so conspicuous in the 

 stalks of Vorticella, evidently correspond to the Elementar-Granula 

 (Greeff, '71) or cyto-microsomes. Entz figured them as arranged in 



