Natural History of the Vorticellae. 395 



external aperture of the alimentary canal (buccal aperture) 

 situated on the margin of the peristome (PI. XVI. fig. 1, w), 

 and here, for the most part, again thrown back in an eddy 

 towards the opposite side, whilst only a comparatively small 

 quantity passes into the vestibulum (pharynx). But even of 

 these last most of the particles are again expelled from the 

 deeply excavated bottom of the vestibulum, in which process 

 the above-described valve-like partitions in the cavity of the 

 vestibulum (pharynx) conduct the two opposite currents. (See 

 PL XVI. fig. 2, in which the arrows indicate the different di- 

 rections of the currents caused by the partitions [k & k') and 

 the ciliation.) 



Those coloured particles which have freely passed the ves- 

 tibulum are now generally rapidly forwarded through the 

 canal which follows (figs. 1, 2, o), by means of the cilia which 

 work briskly within it, fall into the funnel {v) and here stop, 

 until this receptacle is gradually completely filled with colom'ed 

 material. At the same time, however, water is of course 

 carried in through the alimentary tube, so that the ball of 

 coloured material appears to be surrounded by a hyaline 

 vesicle. When the cavity of the funnel is more or less tightly 

 filled, its point, which is directed backwards, opens sooner or 

 later (sometimes when only a small quantity of coloured 

 material has accumulated, and then perhaps by the pressure 

 of the water) ; and then the whole of its contents, in the form 

 of an elongated spindle-shaped morsel, glides at first backwards 

 to the bottom of the body-cavity (PI. XVI. fig. l,h,b), to turn 

 forward again in a curve about to the level of its point of issue. 

 On its arrival here we see a small button suddenly make its 

 appearance (fig. 1, h') on the anterior pointed end of the little 

 coloured body ; and immediately afterwards the whole morsel 

 coalesces into a spherical ball. During^ its whole course, the 

 lumen of the canal, opening in front and closing up behind it, 

 may be very distinctly traced. It is well worthy of notice, in 

 connexion with the whole process, that the velocity with which 

 the spindle-shaped corpuscles of coloured material glide over 

 the course just described is quite different from that of the 

 movement of the rotating nutritive jelly {i.e. it is much greater, 

 and uniform throughout), and that this velocity ceases suddenly 

 and indeed at the very moment when the morsel coalesces into 

 a spherical ball in the manner described above. The coloured 

 ball now lies evidently imbedded in the nutritive jelly of the 

 body-cavity, at first still surrounded by a hyaline cyst (water), 

 and is then slowly carried along with this nutritive jelly. 



The change of form and movement of the coloui'cd coi-puscles 

 is so remarkable and sudden that it cannot be explained ex- 



27* 



