440 LORANDE LOSS WOODRUFF AND RH. ERDMANN 



2. The micronucleus 



While these changes are taking place in the macronucleus 

 the micronuclei do not remain unaltered. They move from 

 their accustomed position, which is more or less close to the 

 macronucleus, and migrate in the cytoplasm (fig. 3, pi. 1). 

 The same appearance was noted in non-conjugating Para- 

 maecium caudatum by Calkins and Cull ('07, p. 383), who 

 state that in stages of a pedigreed race, which Calkins calls de- 

 pression periods, the micronucleus migrates in the cytoplasm, 

 and they interpret this as an abnormal condition. In conju- 

 gating animals the migration of the micronuclei at the beginning 

 of the sexual process is described in Paramaecium aurelia by 

 Maupas ('89, p. 212) and by Hertwig ('89, p. 21); in Paramae- 

 cium caudatum by Calkins and Cull ('07, p. 383); and in Para- 

 maecium bursaria by Hamburger ('04, p. 200). This migration 

 seems to be a general phenomenon at the onset of the changes 

 incident to conjugation and occurs also, as described above, in 

 isolated paramaecia before the beginning of the reorganization 

 process. 



The micronuclei in their new position proceed to divide with 

 the result that finally eight are present in the cell. Figure 14 

 (pi. 2) shows a specimen in which there are two solitary micro- 

 nuclei and two groups of three micronuclei. All the micronuclei 

 show a perfectly normal structure but some variation in size is 

 evident. In typical conjugating animals the eight so-called re- 

 duction micronuclei are described by Hertwig and Maupas as 

 all being of the same size, but Maupas did not lay great stress 

 on cytological details so that only Hertwig's statement is of 

 weight. It is probable that the differences of volume shown by 

 micronuclei in the process are due to variations in the amount 

 of nuclear sap preliminary to the cessation of their functional 

 activity. 



It is impossible to determine whether these micronuclei of the 

 animals in the process are actually reduction micronuclei because, 

 here, as in the conjugation of Paramaecium aurelia, it is not 

 possible to count the number of chromosomes. 



