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GENERAL EMBRYOLOGY 



FIG. 119. Cleavage and cell lineage in the Polyclad Turbellarian, Planocera 

 inquilina. From Surface. A. Egg during the first cleavage; side view. The 

 cell C-D is slightly larger than A-B. B. Four-cell stage, from animal pole. C. 

 Formation of first quartet, from right side, showing spiral cleavage (dexiotropic). 

 D. Eight-cell stage, from animal pole. E. Eight-cells dividing into sixteen, 

 showing laeotropic division. The division of the cells of the D quadrant is in 

 advance of the others. F. Sixteen-cells, from animal pole. G. Sixteen-cells, 

 from vegetal pole. 



