INFUSORIA : ENCYSTING PROCESS. 



459 



continuance of their ordinary vital activity. Previously to the for- 

 mation of the cyst, the movements of the Animalcule diminish in 

 vigour, and gradually cease altogether ; its form becomes more 

 rounded ; its oral aperture closes ; and its cilia or other filamentous 



Encysting process in Vorticella microstoma : — a, full-grown 

 individual in its encysted state ; a, retracted oval circlet of cilia ; 

 b, nucleus ; c, contractile vesicle ; — b, a cyst separated from its 

 stalk ; — c, the same more advanced, the nucleus broken-up into 

 spore-like globules ; — d, the same more developed, the original 

 body of the Vorticella, d, having become sacculated, and con- 

 taining many clear spaces; — e, one of the sacculations having 

 burst through the enveloping cyst, a gelatinous mass, e, contain- 

 ing the gemmules, is discharged. 



prolongations are either lost or retracted, as is well seen in 

 Vorticella (Fig. 241, a). The surface of the body then exudes a 

 gelatinous excretion that hardens around it so as to form a 

 complete coffin-like case, within which little of the original struc- 

 ture of the animal can be distinguished. Even after the completion 

 of the cyst, however, the contained Animalcule may often be 

 observed to move freely within it, and may sometimes be caused 

 to come forth from its prison by the mere application of warmth 

 and moisture. In the simplest form of the ' encysting process,' 

 indeed, the Animalcule seems to remain altogether quiescent 

 through the whole period of its torpidity ; so that, however long 

 may be the duration of its imprisonment, it emerges without any 

 essential change in its form or condition. But in other cases, this 

 process seems to be subservient either to multiplication or to 

 metamorphosis. For in Vorticella the substance of the encysted 



