THE INFUSORIA 



185 



out conjugation. The technique by which such results are 

 obtained consists of isolating single paramoecia in a suitable culture 

 medium, like hay infusion, leaving each individual until it has 

 divided once or twice, and then isolating as many of the progen}^ 

 as it is desirable to retain. As division of the cell usually occurs 



Fig. 99. — Encystment and binary fission in paramct'cium. 



A to D, sketches by Curtis from living material observed by MeClendon, showing 

 problematical encystment and emergence a few days later. The animal folded itself 

 together (A) and rotated as shown by arrows. Gradually a covering appeared (/}). Within 

 this the paramoecium seemed to have a truncate outline (C) that persisted for a short time 

 after emergence (D), but disappeared in the course of one or two cell di\'isions as the par- 

 mnecium resumed its normal activities. E and F, binary fission, with dedifferentiation of 

 old gullet and rcdifferentiation of a new one for each daughter cell, and with mitosis of the 

 niicronudeus and amitosis of macronuclexis. 



from one to four times in twenty-four hours, the multiplication is 

 very rapid. If all could be preserved, they would soon produce an 

 inconceivably large mass of protoplasm (c/. p. 548). Although such 

 increase cannot actually occur either in the laboratory or in nature, 

 it is always a possibility as shown by the rapidity of multipHcation 

 often observed in a culture jar that has been "infected" with 

 paramoecia and allowed to stand for several days in the laboratory. 

 P. caudatum, as well as P. aurelia, lends itself to "domestica- 

 tion" by the cultural methods above described. 



In the cell division by which asexual reproduction is accom- 

 plished, the macronucleus divides by a simple elongation and 

 constriction (Fig. 99); the micronucleus, by a special kind of 

 mitosis (f/. Chapter 6, p. 137). As division of the two nuclei nears 

 completion, the cell body becomes constricted near its middle 

 and finally separates into two daughter cells. Meanwhile, one 



