Chap. XIX.] 



VORTICELLA AND PARAMCECIUM. 



349 



beneath the cover glass. Perhaps the most striking and in- 

 teresting point with regard to this ciliary action is the co- 

 ordination of the movements, and their apparently purposive 



FIG. 102. VORTICELLA, PARAMCECIUM, NYCTOTHERUS. 



A. Vorticella extended. D. Free vorticella after fission. 



B. Contracted. E. Embryo vorticella. 



C. Vorticella undergoing fission. F. Paramoecium. 



G. Nyctotherus. 



an. Anal slit. c. /. Contractile fibre, c. v. Contractile vesicle, d. Disc. 

 end. Endoplast. /. v. Food-vacuole. p. a. Potential anus. ps. Peristome. 

 vs. Vestibule. 



nature. This is accompanied in the metazoa by the development 

 of nerve-tissue ; but nothing of the kind can be made out in 

 vorticella. 



If a vorticella be stained with iodine or magenta, the ectosarc 

 is relatively uncoloured, but the cortical layer is stained. And 

 within the cortical layer a band-like structure, before hardly 

 distinguishable, becomes evident by its deeper stain. This is 

 the endoplast (end.}. It is homologous with the nucleus of a 

 simple nucleated cell. 



