306 



BIOLOGY OF THE PROTOZOA 



What is the significance of this third division? The answer can 

 be only speculative at the present time. The absence of definite 

 chromosomes in some cases, e. g., Paramecium, and the occurrence 

 of heteropolar mitotic figures lend some support to the view that it 

 is a differential division whereby male chromatin, as suggested 



Fig. 155. — Uroleptus mobilis, cut during conjugation as indicated. In this case 

 the conjugants were in the prophase stage of the first meiotic division. PXI, history 

 of reorganization without fertilization. (After Calkins.) 



by Schaudinn (1904) is separated from "female" chromatin, the 

 balance between the two being established by union of the wandering 

 and the stationary pronuclei. Such an hypothetical balance would 

 be maintained if there were no interchange of pronuclei and the 

 third division does not take place, a condition realized in what 



