142 



PROTOZOA 



protoplasm it has a honeycombed or alveolate structure, but in 

 this case the alveoli are permanent in their arrangement and 

 position. Hows of these alveoli run under the surface ; and the 

 cilia are given off from their nodal points where the vertical 

 walls of several unite, and wherein the basal granule or blepharo- 

 plast is contained. Longitudinal threads running along the 

 inner walls of the alveoli of the superficial layer are differen- 

 tiated into muscular fibrils or " myonemes," to which structures 



& 





a 



A 



Fig. 50. Ectosarc of Ciliata. a-/, from Stentor coeruleus ; g, Holophrya discolor, a, 

 Transverse section, showing cilia, pellicle, canals, and niyonemes ; b, surface view 

 below pellicle, showing niyonemes alternating with blue granular streaks ; c, more 

 superficial view, showing rows of cilia adjacent to myonemes ; d, myoneme, highly 

 magnified, showing longitudinal and transverse striation ; e, two rows of cilia ; /, g, 

 optical sections of ectosarc, showing pellicle, alveolar layer (a), myonemes (to), and 

 canals in ectosarc. (From Calkins, after Metschnikoff, Biitschli, and Johnson.) 



so many owe their marked longitudinal striation on the one 

 hand, and their power of sudden contraction on the other. The 

 appearance of transverse striation may be either due to transverse 

 myonemes, or produced by the folds into which the contraction 

 of longitudinal fibrils habitually wrinkles the pellicles, when it is 

 fairly dense (Peritrichaceae) ; circular muscular fibrils, however, 

 undoubtedly exist in the peristomial collar of this group. 

 Embedded in the ectosarc are often found trichocysts, 1 analogous 



Sur les Tnchocystes . . . du Paramoecium" Arch. 





1 See Mitrophanow 

 Protist. v. 1904, p. 78 





