PLATE 7 
EXPLANATION OF FIGURES 
78 Two-cell stage, horizontal section; CD dividing. 
79 Four-cell stage; horizontal section taken above the center of the egg. 
80 Same as the preceding, with plane of section below center. 
81 Nine-cell stage, parasagittal section, to right of median plane. 
82 Horizontal section of a nine-cell stage, taken four sections from the top. 
Taken from embryo composed of 21 sections, each eight micra in thickness. 
83 Same as the preceding; sixth section from top. 
84 Same as figures 82 and 83; fifteenth section from top. 
85 Parasagittal section of a twenty-four-cell stage; plane of section little to 
left of median axis. This figure shows the unequal division of the macromere 
D in the formation of the second somatoblast. 
86 Thirty-three-cell stage. Parasagittal section to left of the median plane. 
Shows the formation of the secondary mesodermal cells (m cells) from the pri- 
mary mesoblasts. 
87 About the same stages as the preceding, to show the distribution of the 
yolk in different cells. 
88 Horizontal section of an eighteen-cell stage, fourth section from top. 
Series composed of 20 sections, each eight micra in thickness. 
89 Same as the preceding; seventh section from top. 
90 Taken from series same as figure 88; eighth section from top. 
194 
