CHAPTER XIX. 



VQRTICELLA AND PARAMCECIUM. 



VoimCELLA, the bell-animalcule, has a delicate clear trans- 

 parent wine-glass or bell-shaped body, carried at the end of a 

 longer or shorter elastic thread-like stalk or pedicle. Within 

 the transparent outer sheath of this stalk is a central contractile 

 thread or fibrilla (c. /.), disposed in an extended spiral form. 

 In some of the largest forms, and under the highest powers, the 

 sheath is seen to be continuous with the thin transparent outer 

 wall of the body called the cuticle. The contractile thread is 

 seen to be continuous with a delicate contractile myophan 

 layer that passes up into the walls of the body and underlies 

 the cuticle. These constitute the ectosarc. Beneath this, and 

 perhaps hardly separable from it, is the cortical layer, which 

 passes insensibly into the more fluid central substance of the 

 body. These constitute the endosarc. 



That which answers to the rim of the wine-glass is known as 

 the peristome (Fig. 102, A.,ps.). ' It is somewhat thickened and 

 turned outwards, and is beset with cilia. Within the bell-shaped 

 opening of the wine-glass is the disc, the edges of which are 

 richly ciliated. The disc is, however, not large enough to fill 

 the opening of the wine-glass, and is attached to one side. Thus 

 there is left a crescent-shaped space, the oral fossa or vestibule. 

 Into this a branch of the ciliary wreath descends. It passes 

 obliquely downwards towards the centre of the bell, thus passing 

 beneath the disc, and gradually narrows till it ends abruptly. 

 An anal aperture is described as opening into the vestibule, but 

 it is perhaps rather a weak spot, or potential anus (p. a.). 



Within the body, close to the vestibule, is a single spherical 

 contractile vesicle (c. v.). This may be seen slowly to enlarge until, 



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