THE CELLULAR BASIS 



173 



Fig. 41. Nokmal akd Inverse Symmetry of the 3d, 4th, 

 Sth and 6th Cleavages. The cells la-l<i, Sa-Sd and 3a-3d give 

 rise to aU the ectoderm; id or M gives rise to mesoderm; 

 A, B, O, D to' endoderm. 



