458 



GARY N. CALKINS 



The conjugating pairs which were cut at this period and which 

 came from the same material as the Z series gave rise to the 

 VXl series, the VX2 series, the VX3 series, and the XZ2 

 series. The conjugating pairs which gave rise to two of these 

 series (VXl and VX2 series) were in the parachute stage of the 



Fig. 7 Conjugating pair in the same stage as that which gave rise to the 

 VX3 series. Both pronuclei are present, but are not yet fused in either indi- 

 vidual. For the VX3 series the pair was cut as indicated, the left individual 

 being cultivated. 



first maturation division at the time of cutting (cf. fig. 1). A 

 third pair giving rise to the VX3 series was cut during a late stage of 

 conjugation and after the interchange of pronuclei but prior to 

 the fusion of the pronuclei (fig. 7). In this case, therefore, con- 

 jugation was completed so far as the nuclear make-up was con- 

 cerned. The XZ2 series, finally, came from an individual ex- 



