236 



GENERAL EMBRYOLOGY 



FIG. 112. Cleavage in the Nemertean, Cerebratulus marginatus. From 

 Korschelt and Heider, after Zeleny. X 216. A, B. Two- and four-cell stages 

 in side view. C. Four-cells, from animal pole. D. Eight-cells from vegetal 

 pole. E. Eight-cells, side view. F. Sixteen-cells, side view. G. Twenty-eight 

 cells, side view. H. Twenty-eight-cells from vegetal pole. For explanation of 

 lettering, see p. 248. 



