528 



BIOLOGY OF THE PROTOZOA 



by Schaiidinn (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 

 Woodruff and Erdmann (1914) called endomixis (see p. 540). 

 Experimental evidence leading to definite conclusions has not yet 

 been advanced. Calkins (1921) made an attempt in this direction 

 by cutting conjugating pairs of Urolephis vwbilis in such a way that 



Fig. 



219. — Uroleptus mobilis, conjugation. The interchange of pronuclei, 

 preceded by a characteristic "attraction sphere." (After Calkins.) 



:>ach 



the two migrating pronuclei were removed while the two individ- 

 uals, now separated, possessed only the stationary pronuclei (Fig. 

 220). These individuals were then followed in cultures, the process 

 of reorganization was completed, the cells regenerated perfectly, 

 and in successful issues, normal rejuvenescence and a typical life 

 history resulted. The crucial point, so far as the present matter 

 is concerned was not determined, viz., from what elements were the 

 new macro- and micronuclei derived? Did the stationary pro- 

 nucleus in its "imbalanced" condition give rise to the new nuclear 

 elements as it would ha^e done were it an amphinucleus? Was 



