232 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
Let us examine still another series of drawings (Figs. 35—42, Plates 
VI. and VII.) made from the living egg, which in this case is viewed 
from the ventral side and a little obliquely. The polar globules of 
course are not seen, since they lie on the opposite side of the egg. 
Neither is the point of view a favorable one to bring the posterior polar 
regions clearly into profile as in the series last examined. 
Figure 35 (Plate VI.) shows the 4-cell stage; Figures 36 and 37, 
successive views of the 8-cell stage; and Figure 38, a 12-cell stage, the 
four cells of the ventral hemisphere having divided in this case a little 
earlier than those of the dorsal hemisphere. "This is unusual, for the 
difference in rate of cleavage of the cells of the two hemispheres com- 
monly first appears, as we have seen in the three series previously 
examined, in passing from the 16-cell stage to one of 24 cells. 
Figure 39 (Plate VIL.) gives a view of the egg five minutes after the 
stage shown in Figure 38 had been reached. It represents the 16-cell 
stage. A drawing made five minutes later still is shown in Figure 40, 
&nd one made ten minutes after that is shown in Figure 41. 
In the last mentioned figure, the cells of this uppermost hemisphere 
are seen to have again become rounded in outline preparatory to the 
next cell division, Spindles are already visible in them, as indicated by 
the arrows, those last to appear being the ones in the small cells 
(0*2, D>”) at the lower margin of the figure. The subsequent division 
was about a minute later in these two cells than in the others of the 
same hemisphere; this is regularly the case in the cell division which 
leads to the 24-cell stage. 
Figure 42, the last of the series, will be at once recognized, by one 
who has read my preliminary paper, as a ventral view of the 24-cell 
stage. (Of. Plate IX. Fig.51.) The posterior end is clearly marked by 
the small cells 0%, D*?, A re-examination of Figures 36 and 37 
(Plate VI.) shows that the rule previously stated for orienting the egg 
at the 8-cell stage is again exemplified in the case of this series, for in 
the existence during karyokinesis of astral fibres which attach to the cell wall at 
particular points and by their contraction depress its surface. 
Such an explanation seems to me inadequate, at least for this case; first, because 
I have seen no evidence of the existence of astral fibres in karyokinesis ; secondly, 
because at successive cleavages the prominences appear in the same structurally 
peculiar region, whether the karyokinetie spindle is directed toward that region — 
as the explanation of Van Beneden et Julin would imply — or not (see Plate VIII. 
Fig. 47) ; thirdly, because astral fibres, if present, should appear in every blastomere 
at karyokinesis, but I have been able to discover these peculiar prominences only 
in the particular regions already described. 
