168 CONJUGATION, MATURATION, AND FERTILIZATION 



by longitudinal but by transverse division, and this division is hetero- 

 polar, so that the resulting nuclei are of different sizes. The smaller 



FIG. 72 



B 



C 



D 



The micronucleus of Paramecium aurelia during conjugation. A, concentration of chro- 

 mosomes after the crescent phase. Accumulation of kinoplasm at upper pole; B, early 

 anaphase of first maturation division; C, late anaphase of first maturation division; D, 

 prophase of second maturation division. (After Calkins and Cull.) 



is the migratory nucleus, the larger the stationary. Each migratory 

 nucleus wanders through the connecting bridge of protoplasm and 

 fuses with the opposite stationary nucleus, the fusion beginning at one 



