B 



Fig. 173, A, B. — Cleavage stages of Tubifex. A, eight-cell stage. B, later stage, showing 

 2da.nd4d{M) (after Penners, 1922). C-£, cleavage stages of leech, Clepsine { = Glossiphonia); 

 C, early stage, showing 2d (first somatoblast) and jD (second somatoblast or mesoblast) ; D 

 later stage, showing E, E, E, E, products of 2d, and M, M, the mesoblasts, products of 3D; 

 E, ectodermal teloblasts and germ bands from 2d, surrounded by heavy line, and mesoblasts, 

 M, M (after Schleip, 1914(7). 



