116 GERM-CELL CYCLE IN ANIMALS 
behave differently from those at other points, since 
they do not remain to form part of the blastoderm 
but continue to migrate until they have become 
entirely separated from the rest of the egg. During 
this process each of the sixteen nuclei that act in this 
way becomes surrounded by a halo of granules — 
part of the pole-disc. Then cell walls appear and 
sixteen primordial germ cells result. These form a 
group at the posterior end, each member of which 
divides twice, thus producing sixty-four germ cells 
in all. During these divisions, which are mitotic, 
the pole-dise granules appear to be equally distrib- 
uted between the daughter cells (Fig. 37, B). 
A rest period then occurs, as far as cellular multipli- 
cation is concerned, during which a ventral plate, 
which later grows into the germ band, develops on 
the ventral surface of the egg. Asin Miastor the 
germ-band pushes around on the dorsal surface 
and the group of sixty-four germ cells is carried 
along with it. In the meantime the germ cells 
begin to migrate from the amniotic cavity in which 
they lie through a sort of canal at the bottom of a 
groove in the germ-band and thus make their way 
inside of the embryo (Fig. 37, F). That the germ 
cells actually migrate and are not simply forced 
about by the surrounding tissues seems certain since 
they are ameboid in shape and pseudopodia extend 
out in the direction of their movement (Fig. 37, F). 
After penetrating into the embryo the germ cells 
become separated into two groups. It was difficult 
to count the number in each group, but many 
