Branch Protozoa 7 



fully, to see the contraction : as the round spot dis- 

 appears see the radiating canals surrounding it. Then 

 see the expansion by which the vacuole resumes its 

 former shape and size. 



IX. — The egestion of indigestible material may sometimes 

 be seen by patient observation. Watch one or more 

 particles that have completed the circuit which the 

 food-balls follow, and have come to rest near the pos- 

 terior end of the body. If you are fortunate, you will 

 see a slight movement of the inner protoplasm, and the 

 particles in question will suddenly be seen lying on the 

 outside of the animal. As no opening in the body 

 wall is visible, it is evident that the particles passed 

 through a temporary opening. Since this usually takes 

 place at the same spot, it is probable that the body wall 

 is adapted at this point to the performance of this 

 function. 



X. — Stain the Paramecium with iodine by putting a drop of 



the coloring-matter on the slide, and drawing it under 

 the cover glass with blotting-paper. This will bring 

 into view a large nucleus, generally near the gullet: 

 and perhaps also the smaller micronucleus, lying beside 

 the nucleus. 



XI. — With a fresh mount, focus carefully along the side 

 of the body to see the short, dark, oval trichocysts, per- 

 pendicular to the surface. Run a Httle dilute acetic 

 acid under the cover glass, and watch the long, hair- 

 like processes — the trichocyst threads — thrown out 

 from the surface of the body. 



XII. — Should you see one of the Paramecia with a con- 

 striction on each side of the body at the middle, 

 observe it closely : it is undergoing fission, the simplest 

 method of reproduction employed by this species. 



