1922] McDonald: On Balantldium coli and Balantidium sms 265 



ridges and grooves, the cilia passing tliroiigh tlie bottom of the latter, 

 but this condition is not due to longitudinal thickenings in the pellicle 

 itself, but to the fact that it is closely applied to the ectoplasm which 

 is thus furrowed. It can often be separated in "blisters" from the 

 ectoplasm by tannic acid or weak alcohol, and when thus removed it 

 shows regular longitudinal rows of perforations through which the 

 cilia pass out from the ectoplasm. In this condition its transparency 

 is very evident. The pellicle is not extremely impervious. For 

 instance, when the active animals are introduced into normal salt 



cir. oes. f. 



or. pi. f. \ i^. 



Fig. J. The neuromotor apparatus of the adoral region, auterior view. X 2000. 

 ad.eil.f., adoral ciliary fiber; ad. memb., adoral membranelles ; hg.ad.cil., basal 

 granule of adoral cilia; cir. oes. f., eireumoesoi^hageal fiber; oytst., eytostome; 

 mot., motorium ; or. pi., oral plug ; or. pi. f., oral plug fibers ; per., margin of peri- 

 stome. 



solution plasmolysis takes place very quickly, and they present a 

 grotesque appearance as they swim about with several huge depres- 

 sions in their surfaces due to the shrinkage. Intra vitam stains such 

 as neutral red and Janus green also penetrate verj' quickly. Resist- 

 ance to pressure and mechanical change, however, is very marked, and 

 is due to its tenacity and flexibility, both of which qualities are showm 

 when the animal forces itself through an opening much smaller than 

 the normal diameter of its body (fig. K) and also by the extreme flat- 

 tening which it withstands tmder the increasing pressure of the cover- 

 glass when evaporation of the preparation is allowed. As previously 

 mentioned, these qualities indicate that the pellicle is protective and 

 retentive in function rather than supportive or skeletal. 



