PARAMCECIUM. 7 



contain coiled threads of protoplasm which can be projected to a 

 greater length than the cilia. It will require close focusing and 

 decreased light to make out either trichocyst threads or cilia. A 

 weak solution of some irritating fluid, such as osmic or acetic 

 acid, will cause the Paramcecium to discharge the trichocysts. 

 j) The nuclei macronucleus and micronucleus. These are 

 brought out by running a little stain, such as iodine or methyl 

 green, under the cover-glass. Look for the macronucleus near 

 the center of the organism. The micronucleus is much the smaller 

 and is attached to the side of the macronucleus. It is very difficult 

 to observe. 



REPRODUCTION. Look for specimens undergoing fission. They 

 will be more or less constricted in the middle and finally will divide 

 on this line of constriction into two halves, each a new Paramcecium 

 individual. Specimens may also be observed in the act of conjuga- 

 tion. They will be temporarily attached one to the other, buccal 

 groove to buccal groove. After an exchange of nuclear substances, 

 they will separate and each individual will undergo fission. 



Exercise i. Draw one or more Paramcecia, showing all the details of 

 structure you can make out. If opportunity offers, sketch individuals 

 in the process of fission or of conjugation. 



HINTS ON COLLECTING. As suggested in the paragraph on habitat, 

 Paramcecia may be secured by making cultures of hay or dead leaves 

 in jars of water. More typical specimens can usually be obtained, 

 however, by the method of collecting and disposing water plants men- 

 tioned in the notes on the Amoeba. Submerged sticks, leaves, and bits 

 of bark from the edges of ponds or streams will also yield plenty of the 

 animalcules when placed in jars in the laboratory. Remove snails, 

 water beetles, or other large organisms from the jars, and keep the 

 latter partially covered with panes of glass to prevent too rapid evapo- 

 ration of the contained water. 



