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 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 wholly 

 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 z 



or Trichoda, and Oxytricha, 



Plate III. No. 71. 



Monadid^e. — Monads. — 



These are amongst the 



smallest atoms of matter 



possessing the mysterious 



principle of life, discernible A^. 



by the highest magnifying f J*&>& 



power of the microscope. 



Minute, however, as they 



are, no one can say that they 



do not derive their suste- _._ 91S 



nance by preying on animals x> Fibri0 spirina , 2 , Mcmophom jubei- 



even less than themselves, taios • near whi ° h au enlarged view o! 



as larger ones of the same 



species do upon them. 



lata ; 



one is shown. 



