668 ' ORDER PERITRICHA. 



ciliary wreath, the right limb of which descends into the oral or vestibular 

 fossa, the left one obliquely elevated and encircling the so-called rotatory or 

 ciliary disc ; the entire adoral wreath contained within and bounded by a 

 more or less distinctly raised annular border— the peristome — between 

 which and the elevated ciliary disc, on the ventral side, the widely 

 excavated oral fossa or vestibulum is situated ; the vestibulum further con- 

 tinued into a conspicuous cleft-like pharynx, and finally terminating in a 

 narrower tubular oesophagus, the junction of which with the pharynx 

 exhibits an ovate and thick -walled dilatation ; anal aperture opening into 

 the vestibular fossa, the upper wall of this same fossa usually bearing 

 apparently a more or less distinct setose appendage known as the vesti- 

 bular seta or "sole de Lachmann" ;* contractile vesicle single, spherical, 

 situated close to and debouching into the vestibulum ; endoplast more or 

 less elongate and band-like; zooids multiplying by longitudinal fission, 

 and gemmation, and by the development of germs through the disruption 

 of the endoplast. Inhabiting salt and fresh water. 



The VorticellcB or " Bell- Animalcules " include, perhaps, the most familiar and 

 graceful representatives of the entire class of the Ciliata. All the members of the 

 genus are readily distinguished by their transparent wineglass- or bell-shaped bodies 

 and accompanying elastic, thread-like pedicles. These organs of attachment during 

 life are in many species in an almost constant state of alternate contraction and 

 prolongation, a circumstance which, in connection with a large colony of these elegant 

 microscopic beings, produces a spectacle of unparallelled beauty and activity. The 

 details of the adoral system, and more especially those relating to the cesophageal and 

 pharyngeal regions as here embodied, have been demonstrated more particularly by 

 Richard Greeff,t and are now admitted as fundamentally identical throughout all the 

 members of the VorticeWuice. The central muscular thread or fibrilla that gives to the 

 stalk of Vorticella its characteristic power of contraction is, as indicated by so early an 

 authority as Ehrenberg, disposed in an e.Ktended spiral form within its hyaline outer 

 sheath, and is also now demonstrated to be continuous with a delicate muscular 

 sheet or layer that passes up into the walls of the body and immediately underlies 

 the cuticle. More correctly, the pedicle in its entirety may be described as an 

 attenuate posterior prolongation of the subcuticular muscular or myophan system, 

 enclosed throughout its length, as in the body, within a tubular sheath of the 

 hyaline, structureless cuticle. In diverse species of the genus Vorticella a con- 

 siderable amount of variation is found to exist in the ultimate construction of the 

 central muscle-like fibre of the characteristic contractile pedicle. In many of these, 

 as seen under high magnification, a coarse granulation of this element, sometimes 

 produced more conspicuously along one edge or in a spiral manner around the 

 central axis, is distinctly visible ; while in some few, such as Vorticella picta and 

 V. appuncta, larger refringent corpuscles of a brilliant hue are found imbedded in 

 it. In Vorticella ncbulifera, as represented by Everts, see Woodcut, p. 674, 

 this central contractile fibrilla exhibits a longitudinally striate pattern ; while in 

 V. margaritifera, according to De Fromentel, it is distinctly striate in a transverse 

 direction. In addition to the longitudinal muscular fibrilL-e, GreefF has endeavoured 

 to show that the trans^Tse stris that form so conspicuous a feature in many repre- 

 sentatives of the genus are also of a muscular character, and describe a continuous 

 and closely set spiral convolution around the animalcule's body. This last inter- 

 pretation is not, however, elsewhere supported ; ovenvhelming evidence, on the 



* For a more detailed account of this append.ige, see family Vorticellidae, p. 656. 

 t " Untersuchung iiber den Bau und die Naturgeschichte der Vorticellen," ' Wiegmann's 

 Aicliiv,' Bd. xxxiii., 1S70. 



