OF ANIMALCULES. 163 



genus Urceolaria, when the anterior cilia are alone ob- 

 served. Besides those already mentioned, there are 

 many other changes in its form : sometimes it stretches 

 itself out in length, and becomes cylindrical, so that it is 

 readily mistaken for a species of the genus Enchelis (see 

 fig. 223) : in this condition, one or both ends bend them- 

 selves while it is swimming past a hard body : it sepa- 

 rates transversely in twain. 



The next method of propagation is by the bud formation, 

 which is not confined either to the animalcules with or 

 without a stem : in the latter case, it is shewn at figure 

 218, and a young one, just separated, below it. It passes 

 through a variety of shapes, moves briskly in the water, 

 and forms the genus Ophrydia of Bory St. Vincent. 

 Ehrenberg has divided this species into two varieties, 

 founded on the shape of the bell : when they are nearly 

 globular, he calls them campanulata, as figure 204, and 

 pyriformiSy Avhen pointed, like figure 211 ; they differ in 

 size from l-200th to l-900th of an inch. 



355. VoRTicELLA cltrina resembles the preceding, but 

 is much larger : like it, it possesses two concentric circles 

 of cilia, and the mouth aperture is situated between them, 

 and not in the centre. Figures 200 and 201 shew this 

 creature magnified in the same proportion (380 times) ; 

 in them may be perceived the two concentric circles of 

 cilia, and the polygastric sacs, which are connected by a 

 common tube (see fig. 202), terminating near the mouth. 

 These facts are easily verified by means of coloured sub- 

 stances, owing to their superior size. Its shape varies 



M 



