The Cellular Basis 



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FIG. 71. NORMAL AND INVERSE SYMMETRY OF THE 30, 4TH, STH AND 6TH 

 CLEAVAGES. The cells la-id, 2a-2d and sa-sd give rise to all the ectoderm ; 

 4d or M gives rise to mesoderm ; A, B, C, D to endoderm. 



