PLATE, 2 
EXPLANATION OF FIGURES 
21 Nine-cell stage, viewed from the right side. 
22 Same stage as the preceding, from the upper pole; spindles for the second 
generation of ectomere are forming. 
23 The same stage from the ventral pole. 
24 Twelve-cell stage from the upper pole; spindles for the third generation 
ectomeres are forming. 
25 Thirteen-cell stage from the left side; the cell d? nearly formed. 
26 Same stage as the preceding from the right side; the embryo is consider- 
ably elongated. 
27 Fourteen-cell stage from the right side; X dividing to form x'. 
28 Same stage as the preceding, ventral view. 
29 Fifteen-cell stage from the upper pole; c* budded off symmetrical with d?. 
30 Fifteen-cell stage from the left side; upper pole turned considerably to 
the left. 
31 Same stage as the preceding from the right side; the small cell x! is drawn 
out between c* and X. : 
32 Fifteen-cell stage, ventral view, as a transparent object, with the position 
of all the cells indicated; drawn from a prepared specimen, cleared in xylol. 
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