164: THE MICROSCOPE. 



nevertheless a hollow tube, through the entire length of which runs a 

 muscular thread of still more minute diameter. When in activity, and 

 secure from danger, the little Torticella stretches its stalk to the utmost, 

 whilst its fringe of cilia is constantly drawing to its inouth any luckless 

 animalcule that may come within the influence of the vortex it creates; 

 but at the least alarm the cilia vanish, and the stalk, with the rapidity 

 of lightning, draws itself up into a little spiral coil. But the Vorticella 

 is not wholly condemned to pass a sort of vegetable existence, rooted, 

 as it were, to a single spot by its slender stalk ; its Creator has fore- 

 seen the probable arrival of a period in its existence when the power 

 of locomotion would become necessary, and this necessity is provided 

 for in a manner calculated to excite our highest admiration. At the 

 lower extremity of the body of the animal, at the point of its junction 

 with the stalk, a new fringe of cilia is developed; and when this is 

 fully formed, the 'Vorticella c[uits its stalk, and casts itself freely upon 

 its world of waters. The development of this locomotive fringe of 

 cilia, and the silbsequent acquisition of the power of swimming by the 

 Vorticella, is generally connected with the propagation of the species, 

 which, in this and some of the allied genera, presents a series of most 

 curious and complicated phenomena. 



The Vorticella possess means of propagation which is denied to 

 other Infusoria, with the exception of a few nearly allied genera, 

 although we shall meet with it again in other classes of animals. The 

 mode of reproduction is called gemmation. It consists in the produc- 

 tion of a sort of bud, which gradually acquires the form and structure 

 of the perfect animal. In the Vorticellm, these buds, when mature, 

 quit the parent stem after developing a circlet of cilia at the lower ex- 

 tremity, and fix themselves in a new habitation in exactly the same 

 manner as the individuals produced by the division of the bell. 



At an earlier or later period of their existence, the Vorticellce with- 

 draw the disc surrounded by cilia, which forms the anterior portion of 

 their bodies, and contracting themselves into a ball, secrete a gela- 

 tinous covering, which gradually solidifies, and forms a sort of capsule, 

 within which the animal is completely inclosed. By this process the 

 little animal is said to become encysted; and at this point of its history 

 it is seen to be more complicated. Sometimes its further progress 

 commences by the breaking up of the nucfeus into a number of minute 

 oval discs, which swim about in the thin gelatinous mass into which 

 the substance of the parent has become dissolved. The body of the 

 parent animal inclosed within the cyst now becomes apparently divided 

 into separate little sacs or bags, some of which gradually acquire a con-. 



