INFUSORIA. 57 



to the simple alimentary apparatus. It should 

 also be mentioned that the spiral line commenced 

 by the circlet of cilia is continued by the vestibu- 

 lum and oesophagus, the longitudinal axis of which 

 may be considered as nearly parallel to the plane of 

 the ciliary disk. The position of the pharynx, on 

 the other hand, is perpendicular to this plane, so 

 as almost to correspond with the general axis of the 

 body. 



Externally, the Vorticella is invested wdth a thin 

 membranous integument or * cuticle ' (l), within 

 which is placed the ' parenchyma of the body ' 

 sometimes known as the ' cortical layer.' In the 

 substance of the latter may usually be seen the 

 ' contractile vesicle ' (/c), which lies close beneath 

 the cuticle, near the anterior extremity of the 

 body. In contact with the parenchymatous layer 

 may also be detected the peculiar band-like body 

 termed the ' nucleus ' (z^), the position of which 

 would seem to vary in different individuals. The 

 ' stalk' of the Vorticella consists of a tubular 

 prolongation of the cuticle, having its longitudinal 

 axis traversed by a peculiar contractile filament 

 (/z.), which is regarded by some observers as the 

 produced apex of a special contractile layer, distinct 

 from the * parenchyma of the body.' 



By the rapid motion of its vibratile cilia the 

 Vorticella is enabled to create currents in the sur- 

 rounding water, by means of which any alimentary 

 particles that may be floating therein are brought 

 into the neighbourhood of the vestibulum. Some 

 of these are rejected, whilst others are quickly 

 propelled through the ciliated oesophagus into the 

 pharynx, where they usually remain until a suflfi- 

 cient number become aggregated into a single mor- 



