PHENOMENA ACCOMPANYING FERTILIZATION 



521 



shortening of the long axis of the crescent. Calkins and Cull 

 (1907) and Dehorne (1920), however, find that the division center 

 or achromatinic substance which forms the poles of the spindle 



( 



mB-^ 



D 



Fig. 215. ^Paramecium caudatum; A, B, C, stages in the first meiotic division 

 during conjugation; D, prophase of second meiotic division. (After Calkins and 

 Cull.) 



migrates from its apical position in the crescent to the center of 

 the convex side, and that this new position marks one pole of the 

 spindle (Fig. 215). 



