78 LABORATORY MANUAL FOR ELEMENTARY ZOOLOGY 



farther and farther apart from each other, drawing out the connecting band 

 into a thinner and thinner thread which finally ruptures. The division of the 

 micronucleus is completed very early in the process of fission. 



(2) Middle fission: The micronucleus is completely divided and one of its 

 halves will be found near each end of the animal. The meganucleus is separat- 

 ing into two halves connected by a slender strand. A transverse constriction 

 is present across the center of the cell. 



(3) Late fission: The division of the meganucleus has been completed. The 

 cytoplasmic constriction has divided the cell nearly or completely in two, but 

 the two halves still cling together. Each half has regenerated those structures 

 which it lacked. The whole process of fission requires in life about one half an 

 hour. The daughter-cells at first smaller than the normal Paramecium soon 

 attain adult size and proportions. 



b) Conjugation: Look over the slide for cases in which two Paramecia are 

 united by their oral grooves. Draw. It is not practical for beginning students 

 to study the stages of the conjugation process but the texts should be consulted 

 for this information (Hegner, pp. 68-73). 



5. General considerations on the Paramecium. Is Paramecium more dif- 

 ferentiated than Amoeba? In your answer, compare in detail Amoeba and 

 Paramecium as to defmiteness of form, organs of locomotion, place of ingestion 

 and egestion of food, etc. In what part of the protoplasm, ectoplasm, or endo- 

 plasm has the greater degree of differentiation occurred? Can you give a reason 

 for this? What does Paramecium gain by its more complex structure? 



D. GENERAL STUDY OF PROTOZOAN CULTURES 



In order to obtain Protozoa in abundance it is necessary to cultivate them in 

 a food-containing solution, which is called a culture. Such cultures are made by 

 adding boiled grain, hay, bread, pond weeds, etc., to a considerable quantity of 

 water; bacteria from the air fall into the culture, flourish there upon the food 

 material which was put into the culture, and furnish food for the Protozoa, 

 which are added to the culture from a natural source, such as pond water. Owing 

 to the abundance of bacteria in such artificial cultures the Protozoa increase 

 by division until enormous numbers of them will be present in a relatively small 

 quantity of water. 



Besides bacteria, yeasts, fungi, and other low plant forms and Protozoa, small 

 multicellular animals also occur in the cultures, and a hasty study will be made 

 of them also. 



Obtain a drop or two of water from Protozoa cultures which are supplied; 

 cover, examine, and identify as far as possible the forms present. Sketches of 

 the more interesting ones are desirable if time permits. In the case of Protozoa 

 particular attention should be paid to organs of locomotion and specializations 

 of structure. 



