PLATE XXXIV. 
Figs. 5-6. Ctenolabrus 64-cell stage. Fig. 5 from above, Fig.6 from below. Both are in about 
(21-22) the same state of division. In [the preparation used for] Fig. 5 the central cells are stained 
* browner (osmic) than the marginal cells, and their distinction was only somewhat less noticeable 
in [the view shown in] Fig. 6. For this reason and for convenience of analysis, I have given 
heavy outlines to the central cells, and dotted outlines to the cells seen through the exposed 
surface. 
I see no reason to doubt that the lettering in Fig. 6 is precisely as it should be in relation to 
the lettering of Fig. 4 of the previous stage. In Fig. 5 there is no obscurity except with regard 
to which ones of the marginal cells represent pe and rc. However as pc of the left side is cer- 
tainly identified, it seems probable that [the numeral] 5 [between 2 and 3 of the anterior mar- 
ginal cells], represents pe of the right side. If these two are correctly identified then there can 
be but little doubt in regard to re—re. 
In both figures, assuming the division completed, we have thirty-six cells in the margin and 
twenty-eight in the center. Of the thirty-six cells, eighteen lie above (obliquely) the other 
eighteen, the eighteen of the upper surface, lying for the most part nearer the center, while the 
eighteen of the lower layer stretch away farthest from the center, extending out so as to present 
one half or more of the upper surface to view. Although Fig. 6 exhibits considerable variations 
from the radial direction of the nuclear figures which prevails in Fig. 5, still the direction is such 
that in the majority of cases the inner pole of the figure lies nearest the upper surface, so that 
the division is not horizontal, but oblique. The pole nearest the observer is more strongly 
shaded in both cases. 
It is very interesting to note that the outer poles in many cases lie extremely near the margin, 
and, particularly in Fig. 6, one can see that the marginal daughter nuclei lie very near the under 
surface — yolk surface — of the cap. Also it is interesting to note that the marginal cells often 
pass into the pellicle with diffuse or blended outline. 
May not the marginal cells already be considered as endoderm and the upper marginal as 
mesoderm? It is quite certain that all the central cells represent ectoderm. 
It is important to note that in all these stages, the two intermediate cells (i) maintain 
uniform relations and always divide horizontally in passing to 64-cell stage. This confirms 
the view that the embryonic axis coincides with first plane of cleavage. 4 
Again a portion of re (6 in Fig. 6) lies in the floor while the marginal portion lies mainly above 
the cells 3 and 4. The left cell rc also divides obliquely, one half showing in the floor. In 
Fig. 5 right re lies wholly in roof, left rc lies wholly in margin. ; 
In Fig. 5 left pe touches the floor at its right end, while right pc lies in margin. In Fig. 6 
right pe lies mainly above 2 and 3 and left pe divides obliquely, one half showing in the floor. 
The nuclei when seen frontally, look like a line of large elongated granules. Viewed from the 
pole they generally present the form of a ring of granules. The achromatic poles are sometimes 
very plain. Some nuclear rays reach beyond the outline of marginal cells, into the pellicle. 
[Fig. 6, no. 1 in anterior row of cells]. 
Vacuoles are seen only in the outlines of the roof-cells — nowhere in the floor-cells; they are 
very neat in both preparations but have been omitted from the figures. 
The cleavage-cavity cannot be traced with certainty; possibly it no longer exists. 
In a 64-cell stage of same set, but 30 min. later, I find two of the marginal cells, at the fore 
or hind end of the future axis that have taken on the form and appearance of true endoderm 
cells. 
Most of the preparations on the slide used for Figs. 5 and 6 are in the 32-cell stage. One of 
these 32-cell stages had a remarkable symmetry. 
There were sixteen cells in the periphery and sixteen in the center. The retro-central and 
pre-central cells did not lap but stood abreast, like the pairs of intermediate cells, reaching from 
top to bottom of cap. Thus the cap was two cells deep only in the four central cells. ; 
Endoderm: — Although I believe the 64-cell stage practically settles the endoderm and that 
some of the cells in this stage very often assume the endodermal condition, I think that they 
resume their outlines and keep the marginal position in the cap for some time later. Two 
hours later than Figs. 5 and 6, I find the endodermal wreath more or less conspicuous in all, 
but in some the wreath has not yet included more than a part of the marginal cells. 
