314 LANGENBECK. [Vou. XIV. 
protoplasm of the macromeres is toward the £F group, the cells 
of the AB group, as can be seen by the diagram, would come 
to lie over the lower pole, whereas the cells of the CD group 
would be drawn away from the upper pole and lie on the side 
of the egg, and the whole ventral plate so formed would lie 
eccentrically over the oval egg. Figs. 17 and 18 show an egg 
at this stage. The eleven cells at EF are the descendants 
of the ZF group, the twelfth cell of this group lying beneath 
the surface, as was shown by sections. The end cells of 
the CD group can be seen in Fig. 18 on the side of the 
egg, while the end cells of the AB group cover the lower pole. 
The cells of the EF group will form the head region and the 
dorsal organ. Bessels ('70) is inclined to believe that the dorsal 
organ arises exactly at the same point where the blastoderm 
first appears on the surface of the egg, but, according to my 
observations, it does not appear exactly at this point, but a little 
lower down, as the cells of the ZF group, which are the first 
blastodermic cells to appear, spread during their growth. In 
sections of an egg at this stage cells are seen underneath the 
surface in the ZF region, and I think these are the descendants 
of ef, because the sections of the egg represented in Fig. 17 
show five cells beneath the surface in this region. One of these 
is, I think, the twelfth cell of the ZF group, as only eleven 
were seen on the surface. It is only in this way that the ef 
group can be accounted for. It will be remembered that only 
four cells were derived from this group. Another reason which 
led me to this conclusion is that all the other micromere cells 
are overgrown as the embryo develops and come to lie in the 
lower layer. 
Summary. 
The first cleavage plane appears three hours after the deposi- 
tion of the egg. The three succeeding divisions, vertical, equa- 
torial, and vertical, occur at intervals of an hour each, and after 
this the large macromeres divide synchronously and regularly, 
a vertical cleavage alternating with an equatorial cleavage; 
but the micromeres no longer divide synchronously with the 
macromeres. 
