162 GEORGE W. TANNREUTHER 
Fig. 5 Twenty-four-cell stage in ventral view, to show the division of the 
large macromere D. The larger of the two cells d‘ (M) becomes the ‘second 
somatoblast.’ The smaller cell D, becomes one of the four entomeres; D is 
scarcely visible from the exterior. 
Fig. 6 Same as the preceding, in an apical pole view. 
Fig. 7 Twenty-four-cell stage, ventral view, shows the bilateral division of 
M. D after the bilateral division of M becomes more distinct from surface view. 
Fig. 8 Horizontal section of an early embryo to show spindles in the forma- 
tion of x® from either proteloblast X, X. 
Fig. 9 Horizontal section little later than preceding, to show the small cell 
x!-x®; apical pole view. 
