PHYLUM PROTOZOA. CILIATES 



55 



principally to Paramecium caudatum (Fig. 

 25) and Param.ecium. aurelia. Paramecium, 

 caudatum ranges from about 0.15 mm, to 0.3 

 mm. in length, and Paramecium aurelia 

 from about 0.12 mm. to 0.2 mm. Figure 25 

 indicates the shape of a specimen of P. 

 caudatum. The anterior end is blunt and 

 the posterior end more pointed. The greatest 

 width is behind the center of the body. 



A depression extends from the anterior 

 end, obliquely backward, ending just pos- 

 terior to the middle of the animal; this is 

 the oral groove. The cell mouth (cyto- 

 stome) is situated near the end of the oral 

 groove. It opens into a short tube, the cell 

 gullet (cytopharynx), which passes obliquely 

 downward and posteriorly into the endo- 

 plasm. The side containing the oral groove 



Anterior end 



Cilium 

 Trichocysts 

 Food vacuole 3 



Contractile vacuole 

 Pellicle 



vJral groove - 

 Micronucleus- 

 Macronucleus 



Cell mouth — 

 Cell gullet 



Ectoplasm 

 Endoplasm 



Food vacuole 2 



Bacteria being ingested 



Food vacuole forming. 

 Cell anus^ 



i^JiSlS- 



^■wm^. 





t— ' 



wm, 



Radiating canal of C. vacuole 

 Food vacuole 1 



OJt 



Figure 25. Left, spiral path of a free-swimming paramecium. Note that these animals rotate 

 on their long axes at the same time that they are moving forward. Right, drawing designed to 

 show the structure of Paramecium caudatum. Numbered food vacuoles show progress of digestion 

 and absorption. 



