INFUSORIA. 



411 



information to our former meagre knowledge of these in- 

 teresting forms of organic life. 



Some Infusoria undergo a process of encystation before 

 reproduction by fissure ; that is, they become coated with 

 a secretion of gelatinous matter, which gradually hardens 

 so {is to enclose the body in a "cyst." According to 

 Stein, the process of encystation is sometimes followed by 

 a remarkable succession of phenomena, such as have been 

 observed to occur in the case of Vorticella microstoma. 

 An old "Vorticella loses or retracts its cilia, becomes en- 

 cysted, and finally drops off its stalk. The cyst may either 

 burst and discharge its contents, or become wholly 

 changed into an Acineta-form body. The latter may sub- 

 sequently develop a foot-stalk, assume the ajDpearance of 

 a Fodophyra, or even that of the Acineta tuberosa, 

 Plate III. No. 68. In either case, the band-like nucleus 

 becomes transformed into a peculiar ovate body, somewhat 

 like Nos. 71 or 73, the narrow end of which is provided 

 with a circlet of vibratile cilia, and a mouth leading into 

 an internal cavity, with a contractile vesicle in its interior, 

 Eelations, somewhat similar , 

 to those which connect 

 Vorticella and Acineta, have 

 been stated to exist between 

 other families, as Aspidisca 2 

 or Trichoda, and Oxytricha, 

 Plate III. No. 71. 



Mon adid,e . — Monads. — 

 These are amongst the 

 smallest atoms of matter 

 possessing the mysterious 

 principle of life, discernible 

 by the highest magnifying 

 power of the microscope. 

 Minute, however, as they 

 are, no one can say that they 

 do not derive their suste- 



*%» 



Fig. 218. 



nance by preying on animals 1} vibrio spirilla. 2, Liwnophora flabei- 



even less than themselves, lata; near which an enlarged view 3 f 



as larger ones of the same 

 species do upon them. 



one is shown. 



