248 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
the very intense blue color which they take upon treatment with a 
hematoxylin stain. Their cytoplasm is not homogeneous at this stage, 
but contains numerous large dark-looking granules. The granules are 
undoubtedly yolk granules, and their dark appearance can often be seen 
upon close inspection to be due to an enveloping film of deeply staining 
protoplasm, which often extends out in radial processes, giving the whole 
a star-like appearance. This I believe to be caused by the progressive 
assimilation of the yolk eranules and their conversion into protoplasm. 
In the case of the mitotic cell 47:6 (Fig. 67), and likewise of its mate in 
the left half of the samo Figure, the characteristic mesenchyme stain- 
ing appears only in the more superficial portion of the cell, its deeper 
portion being loaded with yolk granules, which are still almost unat- 
lacked by the protoplasm. Consequently, when the approaching divis- 
ion is accomplished, the sister cells formed will differ from each other 
in appearance, the more superficial one being deeply stained, the other 
being stained scarcely at all. Subsequently, however, the yolk-laden 
cell will come to resemble in appearance its sister cell, and will have 
the same ultimate fate. The nuclei of the mesenchyme cells resemble 
closely in appearance those of the endoderm cells. In the case of e”? 
and d7? (Figs. 65 and 66), the nuelei are relatively small on account 
of recent division. 
7.13 
, 
a’). and. a 
The eight anterior chorda cells (a, Fig. 68; a”, ; 
Fig. 69 ; together with the corresponding cells in the left halves of these 
Figures) resemble closely in shape and stainability the endoderm cells. 
They are smaller, however, and contain nuclei, likewise smaller, with 
less conspieuous chromatic granules (omitted altogether in the Figures, 
as previously explained, to aid in readily distinguishing the chorda cells 
from those of other organs), 
The two posterior chorda. cells (d’™, Fig. 66; C"? [by mistake of 
engraver for c^] Fig. 67) stain more deeply than the anterior chorda 
cells, resembling to some extent their sister cells d7 and 72 (Figs. 65 
and 66), from which they have recently been separated by division. 
However, they are many times smaller than their sister cells, and extend 
less deeply. This difference is connected with the oblique position of the 
spindles in the mother cells (sce d995, Fig, 60), a matter to which atten- 
tion was called in the discussion of the 64-cell stage. 
In the neuro-muscular ring the cells (stippled to distinguish them 
from those of other groups) have about tho same histological character in 
both anterior ( 45-16. Fig, 68; 4*5 Fig, 69; 48%, 498; Fig. T0: together 
with the corresponding cells in the left halves of these Figures) and pos- 
