ACCOUNT OF THE GERM-CELL CYCLE 33 
trated by the case of Amia and Lepidosteus. While 
in the forms that I have studied they are first to be 
observed in the entoderm, I am quite open to convic- 
tion that in other forms they may migrate from this 
layer into the potential mesoderm before the two 
layers are separated, as shown by Wheeler in Petro- 
myzon.” 
Swift (1914) has recently obtained evidence which 
seems to prove that not only do the germ cells of 
the chick migrate by ameboid movements but they 
enter the blood vessels and are distributed by the 
blood stream to all parts of the embryo and vascular 
area. 
The migration of the germ cells has been noted in 
many invertebrates and has been fully described 
in chrysomelid beetles (Hegner, 1909a). In these 
insects the primordial germ cells are segregated at 
the posterior end of the egg at the time the blasto- 
derm is formed (Fig. 36, C). The blastoderm is 
never completed just beneath them, but a canal, 
called the pole-cell canal, remains. Through this at 
a later embryonic stage the germ cells migrate by 
means of ameboid movements. 
*“As soon as the germ cells of Calligrapha have 
passed through the pole-cell canal, they lose their 
pronounced pseudopodia-like processes and become 
nearly spherical (Fig. 37, E); nevertheless, they 
undergo a decided change in position. They move 
away from the inner end of the pole-cell canal, and 
creep along between the yolk and the germ-band. 
Thus two groups are formed near the developing 
D 
