Fig. 6. Successive Stages in the Cleavage and Gastruxa- 

 tion of Amphioxus. A, one cell; B, two cells; G and D, four 

 cells; E, eight cells; F, sixteen cells; O, blastula stage of about 

 ninety-six cells; H, section through the same showing the 

 cleavage cavity; /, blastula seen from the left side showing 

 three zones of cells, viz., an upper clear zone of ectoderm, a 

 middle (faintly shaded) zone of mesoderm and a lower (deeply 

 shaded) zone of endoderm cells; /, section through the same 

 showing these three types of cells; K and L, successive stages 

 in the infolding of the endoderm; cells indicated as in the pre- 

 ceding figure. In all figures except D the polar body is shown 

 at the upper pole. Figs. A-H after Hatschek. a, anterior; 

 p, posterior; v, ventral; d, dorsal; be, blastocoel; gc, gastrocoel. 

 I and J should be reversed to correspond in position with 

 K and L. 



