PLATE 3 
EXPLANATION OF FIGURES 
33 Seventeen-cell stage from the upper pole; spindles in the first generation 
of ectomeres forming. 
34 Twenty-cell stage from the upper pole; cells c'!, d'~! and x? just formed. 
35 Twenty-one-cell stage from the right side; b!!, new cell; this embryo is 
unusually elongated. 
36 Twenty-three-cell stage from the upper pole; d' and x*, two new cells 
formed; embryo considerably flattened. 
37 Twenty-four-cell stage from the ventral side; the unequal division of D 
has just occurred; D partially visible; the cleavage spindle of M forming. 
38 Twenty-five-cell stage, ventral view; division of M complete and the 
spindle for the first bilateral division of X is forming. 
39 Twenty-five-cell stage from the left side. 
40 Twenty-five-cell stage from the upper pole; embryo is nearly spherical. 
41 Twenty-six-cell stage, ventral view. 
42 Same as the preceding, ventro-anterior view. 
43 Twenty-nine-cell stage, same aspect as preceding; a‘, b* and c4 are the 
three new cells formed. 
44 Forty-two-cell stage from the upper pole; increase in number of cells 
due to the rapid division of the ectomeres. 
164 
