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THE AMERICAN NATURALIST [Vol. LI 



observed. (2) The polarity of the rosettes may influence the cells in 

 such a way that those near the center of the ovariole and closest to the 

 zone of differentiation tend to develop into oocytes. (3) Those cells of 

 the rosettes which reach the zone of differentiation tirst are stimulated 

 to become oocytes and by their growth and differentiation prevent the 



4. Constitution of the Oocyte at the Beginning of the 

 Groivth Period 



Very soon after the nurse cells are formed and the 

 oocytes begin to enlarge the main axis of the oocyte in all 



insects seems to be established. The germinal vesicle 

 at the same time changes its position from the center of 

 the cell to a point near the nurse-cell chamber at the an- 

 terior end as described above in Miastor (Fig. 8). At 

 what stage bilateral symmetry becomes fixed has not been 

 determined. 



The oocytes of insects at the beginning of the growth 



