THE PARAMECIUM 75 



longer than the cilia, extending from the surface. These are the 

 trichocysts which are discharged as a result of contact of the animal 

 with the stain. They are structures for defense. Show the discharged 

 trichocysts on part of the margin of your figure. 



Exercise 3. — Ingestion and Food Vacuoles. 



(g) Take a very small drop of water, containing many paramecia, 

 and add an equal amount of water containing India ink obtained by 

 rubbing a bit of an ink stick against the bottom of a watch glass con- 

 taining a little water; or finely powdered insoluble carmine may be 

 used. Study the action of the cilia as they drive the particles about. 

 Watch for a time and see how the particles get into the cell. Can 

 you see the actual "gulping down" of the particles? Does feeding 

 continue regardless of the amount of material ingested? Where are 

 the particles found after ingestion? Trace the course of the food 

 vacuoles as they are carried in the endoplasm. Where do they come 

 to rest? Make a series of three outline drawings of a Paramecium, 

 showing details only in the region of the buccal groove and gullet, to 

 illustrate this process, and write a brief explanation. 



Exercise 4. — The Contractile Vacuoles. 



(h) Mount some specimens in a very small drop of water, holding 

 them in place, without crushing, by the weight of the cover glass. 

 Study the formation and collapse of the contractile vacuoles and of the 

 canals leading to each vacuole. Time the contractions. Compare 

 with the observations of other students. AVrite an accurate descrip- 

 tion, accompanied by four drawings, explaining how the vacuoles and 

 their canals function in discharging fluid from the cell. 



Exercise 5. — Division and Conjugation. 



(i) Individuals are often seen in the process of reproduction by cell 

 division. This occurs by transverse binary fission or mitotic division 

 of the cell into two equal parts. If a dividing specimen is found, it 

 should be kept under observation continuously by moving the slide 

 about. After some minutes it will be seen to separate into two inde- 

 pendent cells, each of which then becomes a perfect individual. The 

 nuclear changes during fission can be observed only in stained mate- 

 rial. Examine and draw a series of demonstrations stained to show: 

 (1) the beginning of constriction in the cytosome, elongation of the 

 macronucleus, and the formation of a mitotic figure in the micronu- 

 cleus; (2) further constriction of the cytosome and macronucleus with 

 separation of the new micronuclei; and (3) a later stage in which di- 

 vision of the cytosome and macronucleus is almost complete. 



