PLATE 3 



EXPLANATION OF FIGURES 



12 Showing the effect when the A and B cell divide in abnormal planes; the 

 ectodermal cells number 8 in this egg. 



13 A slightly later stage of the same ; note that the MSt cell does not lie in the 

 median plane of the embryo. 



14 An egg showdng the effect of the unequal division of the chromatin between 

 the A and B blastomeres. 



15 An egg showing the effect of the tetraster formation in the Si cell. 



16 Showing the Pa and EMSt cell fusing; note particularly the protoplasmic 

 ball projecting from the fusing cells. 



17 Showing the later effect of the fusion of the Po and EMSt cells; note that 

 diminution is taking place in this cell. 



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