26 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
taining the larger yolk granules shown in Figure 7. The larger deriva- 
tive retains its position at the macromere end of the egg (Fig. 19). 
The smaller cell d' is therefore pushed dorsad, and this, together with 
the extension of d*? at the time of the formation of its spindle, dis- 
places the animal pole, marked by the polar cell, still farther toward 
the micromere end of the egg. As a further result, the cells of the 
quadrants A, B, and C are still more compressed dorso-ventrally, so 
that, especially in a*! — c. , the lateral extent is much greater than the 
dorso-ventral (Fig. 19). 
Nevertheless, as Figure 19 shows, the rotation of the future spindle 
axis still continues. The line joining the asters becomes dorso-ventral 
first in the dorsal cells 4 — , while in a** — c*4 the asters are still 
oblique, as shown in c, Figure 19. In quadrant B of this same figure, 
the axis has become dorso-ventral in both cells. 
Now occurs the cleavage of d*?, with still further elongation, shifting 
of the animal pole toward the micromere end of the egg, and resulting 
greater compression of the cells of the quadrants A, B, and C (Figs. 
20-24). Without regard to this, the asters in the cells of these quad- 
rants continue their movements until the future spindle axes are in 
every case dorso-ventral. Spindles are now formed in all of the six 
cells, the spindle being in every case in the shortest axis of the cell 
(Figs. 20-24). 
The conditions at this stage are so significant from a cyto-mechanical 
standpoint, that I have thought it best to analyze and illustrate with 
especial fulness a typical egg at this stage. Figures 20-95 are views 
of a single egg. Figure 20 shows the right side (quadrant C), Figure 
22 the left side (quadrant A), Figure 21 an anterior view (quadrant B), 
and Figure 25 a posterior view (quadrant D). In Figures 23 and 24 are 
given respectively sagittal and frontal optical sections, for comparison 
with the surface views. 
In order to exclude possibility of error, the egg from which the above 
figares were taken was moved about so that the six cells belonging to 
the quadrants A, B, and C occupied successively the middle of the 
upper surface of the egg; careful camera figures of each cell were made 
in this position. Then optical sections were taken in the same way, 
both along the axis in which the spindles lie, and at right angles to 
these. Accurate measurements of the dimensions of the cells could 
thus be made; the results are as follows. 
