34 GERM-CELL CYCLE IN ANIMALS 
coelomic sacs; each group probably contains an 
equal number of cells. The smallest number I 
have counted in one group at this time is thirty; 
the largest number, thirty-four. As there is some 
difficulty in obtaining an accurate count, it seems 
probable that the sixty-four germ cells are equally 
divided and that each germ gland receives thirty-two. 
Some of the germ cells migrate not only laterally 
along the germ gland but also back toward the 
posterior end of the egg, where we find them forming 
narrow strands in the last abdominal segments. 
From this stage on, the germ cells are not very active ; 
they move closer to one another to form the compact 
germ glands. I was unable to determine whether 
the later movements of the germ cells are due to 
an active migration or to the tensions created by 
the growth of the surrounding tissues; the latter 
seems the more probable” (Hegner, 1909a, p. 280). 
It is thus evident that during the blastoderm stage 
the germ cells of this beetle are actually outside of the 
egg. How well this illustrates the theory of primary 
cellular differentiation, that is, the differentiation of 
germ cells from somatic cells, since the two sorts 
are here completely separated, the former constitut- 
ing a group in contact with but not connected with 
the somatic cells. Later, as the germinal con- 
tinuity hypothesis demands, the germ cells migrate 
into the embryo, there to be nourished, transported, 
and protected by the body until they are ready to 
separate from the somatic cells, and thus to give rise 
to a new generation. 
