342 GENERAL HISTORY OF THE INFUSORIA. 



activity, by means of its cilia, which yet remain apparent. Stein mentions 

 this phenomenon in StylonycTiia pustidata (XXIX. 18), and in the encysted 

 embryos or gemmae of Colpoda ; and we know that similar movements precede 

 its revival from its quiescent condition in all cases. 



The cyst-wall is, at least in some exami^les, double, consisting of an outer, 

 finely-granular, softer layer and an inner, consistent, elastic, homogeneous 

 membrane (XXIX. 21, 22, 41, 43). It may be that two such laminae always 

 exist ; for the outer one crumbles away so soon as the enclosed animal prepares 

 to reassume its activity, and it is after the onset of internal changes that 

 most observations have been made upon cysts. The two coats were remarked 

 by Auerbach (ZeitscJir. 1854, p. 431) in Oxytricha PeUioneUa (XXIX. 21-23) ; 

 by Stein in Cliilodon Cucullidus (XXIX. 53, 54), in Stylonycliia ]^ustidata 

 XXIX. 18), and in Nasstda ambigua ; and by Cienkowsky in Nasstda viridis 

 (XXYIII. 67), &c. In Chilodon, indeed. Stein represents several concentric 

 layers to the cysts (XXIX. 55, 56), and states that in this instance the walls 

 acquire no firmness, but remain soft and gelatinous. 



Another pecuharity attaching to cysts in some species, is, that they 

 produce folds or plaits on their surface, and therewith acquire an apparent 

 angular outline, as Stein exhibits in his figures of encjaieii Ejjistylis plkatUh 

 and E. hrancMopMla, where the lines are longitudinal, and in encysted Oper- 

 cidar'ia berberiformis, where they are transverse or annular. 



Again, the cyst-walls are not always smooth : thus, in Nassida ambigua 

 Stein represents them as punctate in longitudinal lines ; in Stylonychia pms- 

 tulata (Midler's Arcliiv, 1856, iv. ; A. N. H. 1857, xix. p. 228) they have 

 stellate markings, and in a small undescribed species of Epistylis a finely- 

 shagreened surface. 



The changes which the encysting animal itself undergoes have been men- 

 tioned generally ; but a few more details, aided by reference to particular 

 examples, are required for a more complete elucidation of them. So soon as 

 the animalcule becomes quiescent within the sac secreted around it, the ciHa 

 which covered the surface, including any of larger dimensions disposed along 

 certain tracts, or upon particular processes, disappear, and have generally been 

 presumed to be destroyed ; however, various obsen^ations are on record which 

 seem to show that this is not universally the case, but that not imfrequently 

 they are merely concealed from view ; and this being so, it becomes ques- 

 tionable whether — especially in the ordinary process of encysting, where 

 only the conservation of the individual is intended — their destiaiction or 

 absorption is the rule. An observation of Stein may be quoted on this ques- 

 tion : — An encysted Chilodon Cucidhdus, after developing several embryos, 

 ceased this process of propagation, redisplayed its cilia as if by simple evolu- 

 tion, and commenced mo\dng within its cyst along ^vith one of its embryos 

 (XXIX. 58). The inference deducible from this particular observation in 

 the case of the encysting-process, even when exercised for the distinct purpose 

 of generation, is greatly strengthened by the oft-repeated observations of the 

 release of the imprisoned beings, by pressure causing the iTipture of the newly- 

 formed cyst, in the possession of their complete figm^e and their ciliary arma- 

 ture. We may add that no proof exists of an actual new formation of ciha 

 upon beings when emerging from their cyst ; aU that can be predicated is, 

 that cilia reappear in their normal positions and arrangement. 



To sketch now the history of the encysting-process by a reference to some of 

 the many examples recorded by various microscopists ; for the act has been 

 witnessed in so many species and genera, that it is assumed to be common to 

 all. The description given by Cohn (Zeitschr. 1 853, iv. p. 267) of the encyst- 

 ing of Trachelitis Ovum may be given as an example (XXIX. 19, 20) : — The 



