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 

 go as 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 whoUj'' 

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

 sequently develop a foot-stalk, assume the appearance of 

 a Podophyra, 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 Nop. 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. 

 Relations, somewhat similar 

 to those which connect 

 Vorticella and Acineta, have 

 been stated to exist between 

 other families, as Aspidisca 

 or Trichoda, and Oxytricha, 

 Plate III. No. 71. 



MoNADiD^ . — Monads. — 

 These are amongst the 

 smallest atoms of mailer 

 possessing the mysterious ^^^^^ ^, ^^^=^^^^,j^^^ ^^^n\^^^^ 



Q^:'>^. 



S'y^\ (i 



•^ 



o 



*.«i^» 



power of the microscope. 

 Minute, however, as they 

 are, no one can say that they 

 do not derive their susle- 



Fig. 218. 



nance by preying on animals j^ vihno spirilla. 2, ucfno-pUra flahd- 

 even less than themselves, ^"^''/g^^^j;^^^"*^^ ^"^ enlarged view of 

 as larger ones of the same 

 species do upon them. 



