358 GENEKAL HiSTOKY OF THE INEUSOKIA. 



Among cysts of the usual form and dimensions, are some in which a sac, not 

 uniformly adherent to the inner surface of the capsule, contains from two to 

 eight, or, more generally, from four to six, oval or reniform secondary sacs, 

 irregular both in position and size (XXIII. 10, 11), and containing a dull and 

 fine or coarse granular matter, wdthin which, again, is a clear (contractile ?) 

 space, but no nucleus is discoverable even when acetic acid is added. Pre- 

 sently these vesicles elongate, and, becoming flask-shaped, protrude their 

 necks through the enclosing sac and the cyst-waU (XXIII. 12, 13), and 

 proceed to discharge their contents (XXIII. 14) through their open extremi- 

 ties ; after which, they corrugate and wither. The discharged matter is 

 composed of a mass of monadiform corpuscles united together in a globose 

 gelatinous mass, the whole of the organic matter filling the cyst being used up. 



A precisely similar act of propagation Stein also witnessed in an encysted 

 Vorticella nehulifera. Cienkowsky (ZeitscJir. Band vi. p. 381) also reports 

 its occurrence in Nassula vindis, Duj. (XXYIII. 65-71); according to this 

 author's researches, the contents of the cysts of Nassula vindis break up 

 into a number of globular cells (XXYIII. 68-70), which soon partake of a 

 certain degree of rotating movement among themselves, develope in their 

 interior a multitude of wdiat he terms swarm-spores, and at a certain period, 

 when mature, severally produce, in turn, a tapering neck-like tubular process 

 (XXYIII. 68, 69), which perforates the softened cyst-waU and gives exit 

 to the spores or germs (XXYIII. 71). This account taUies with that given 

 by Stein of certain Vorticella-cysts. Lachmann has the foUo\\dng remarks 

 on this topic (A. N. H. 1857, xix. p. 238): — " It was only in his most recent 

 observations on Vorticella microstoma, that Stein saw the production of larger 

 globules, ' daughter- vesicles' {Tochterblasen), in the interior of the mother- 

 vesicle ; but pre\iously he had seen nothing of the kind : it must remain 

 uncertain whether he had overlooked them, w^hether, instead of several 

 globules, only one very large one, entirely fiUing the mother-vesicle, had 

 been produced, or whether two different modes of development actually 

 occur in this case. This is the only mode of reproduction of the Infusoria 

 w^hich has hitherto been observed in encysted animals alone ; but some ob- 

 servations made by E. Claparede and myself upon an undescribed vagini- 

 colous Infusorium, indicate that encystation is not a necessary condition 

 even for this mode of propagation." 



The last plan of generative development to be considered is that wherein, 

 according to Stein's hypothesis, the encysted animalcule undergoes an actual 

 metamorphosis, and subsequently, as a rule, produces an embryo wliich, 

 although very dissimilar to the original ciliated animalcule, is nevertheless 

 presumed to be convertible into it after passing through one or more trans- 

 itory phases of existence. 



This cycle of life, or, according to Steenstrup's hypothesis, this " alterna- 

 tion of generation," in the generative acts of ciliated Protozoa, Stein has 

 most diligently sought to establish as a fact, but, in the opinion of most of 

 the best naturalists, has failed so to do. Still the hypothesis is too curious 

 and interesting to be omitted from our description, and, what is more, has 

 been adopted as true by several observers. It will therefore be best, fii'st 

 to set forth Stein's own account, and then to add the remarks and objections 

 of others. 



On some of the branching stems of Epistylis plicatUis, and of E. nutans, 

 Stein encountered not only the ordinary animalcule in full activity and in a 

 contracted state, but also some pear-shaped bodies, presenting merely the 

 ordinary nucleus and a contractile space, without mouth or any remnants of 

 the alimentary tube or of food. On other branches, again, were other 



