Nov2.) AICRODEUVUTOPUS, GRYELOTALPA COSTA. 313 
inner ends, and the blastocoel becoming obliterated. The sec- 
tion shows one of the two cells which have wandered in. Its 
nucleus appears as a dark, homogeneous mass, showing signs of 
disintegration. 
100-cell stage. — The thirty-two large cells all divide once 
more, by vertical cleavages, into sixty-four. I should state here 
that, although I have always spoken of the descendants of the 
four large macromeres of the 16-cell stage as large, I have done 
so merely to distinguish them from the descendants of the 
small macromeres. Somewhat before the 73-cell stage, owing 
to their more rapid cell division, the difference in size has 
disappeared, and in the living egg, as stated by Mlles. Pereyas- 
lawzewa ('88), Rossiiskaya ('88), and Wagner (91), the macro- 
meres and micromeres cannot be distinguished. In the cleared 
egg they are recognized by the different appearance of their 
nuclei and the smaller amount of protoplasm contained in the 
micromeres. 
It will be recalled that in the 16-cell stage A and C were 
flattened against each other, while 6 and PD were forced 
apart by G and H. Because of the obliquity of the second 
cleavage furrow and the flattening of 
the larger macromeres against each 
other, the group of small cells lies 
obliquely on the oval egg, as shown 
in the diagram. Since, as_ stated 
before, no change in the position of 
the cells takes place, their descendants 
have exactly the same position as the 
cells themselves originally had. So 
the AB group lies over the pole near- 
est the EF group, while the CD group 
lies over the opposite pole, and the A and C groups lie near- 
est each other and border the ZF group. At this time the 
protoplasm of all the blastomeres rises to the surface (Fig. 
17). The protoplasm of the macromeres becomes more con- 
centrated, while that of the micromeres spreads over the yolk, 
thus making such a thin layer that only the dark nuclei 
remain visible (Fig. 18). Since the concentration of the 
