456 



GARY N. CALKINS 



The PX7 series therefore behaved like a normal series in every 

 way, despite the facts that the process of conjugation was in- 

 terrupted at the start by cutting and that no nuclear interchange 

 occurred. It not only passed through a normal life-cycle, but 



Yjf5 



Fig. 5 Conjugating pair in the same stage as the pair which gave rise to the 

 X75 series. The two migrating nuclei are at the anterior end. In the pair 

 which gave rise to the X7o series, these were removed by cutting as indicated. 

 The fragment corresponding to the shorter right-hand individual was culti- 

 vated as the X75 series. 



Fig. 6 X75 series. Sketches from the living fragment during reorganization. 



