232 GERM-CELL CYCLE IN ANIMALS 
of the odgonia in Dytiscus a rosette of sixteen cells 
is produced of which one is the ojcyte and the other 
fifteen nurse cells. The rosette thus formed possesses 
a definite polarity coincident with the axis of the 
odcyte which is identical with that which was present 
in the last generation of odgonia. Similarly in 
Muastor (Fig. 12) the polarity of the odcyte is recog- 
nizable as soon as the mesodermal cells, which serve in 
this species as nurse cells, become associated with it. 
The germ cells of other animals also possess a 
precocious polarity, as evidenced by their implanta- 
tion in the germinal epithelium (e.g., Wilson, 1903; 
Zeleny, 1904, in Cerebratulus), the position of the 
nucleus, the formation of the micropyle (Jenkinson, 
1911), etc. This is true not only for the inverte- 
brates, but, as Bartelmez (1912) claims, ‘“‘the polar 
axis persists unmodified from generation to genera- 
tion in the vertebrates and is one of the fundamental 
features of the organization of the protoplasm”’ (p. 
310). Furthermore, experiments with centrifugal 
force seem to prove that the chief axis of the egg is not 
altered when substances are shifted about, but is 
fixed at all stages (Lillie, 1909; Morgan, 1909; 
Conklin, 1910). Bilaterality also is demonstrable 
in the early stages of the germ cells of many animals, 
and, like polarity, seems to be a fundamental charac- 
teristic of the protoplasm. 
It is somewhat difficult to harmonize the various 
results that have been obtained, especially by experi- 
mental methods, from the study of egg organization. 
As the odcytes grow, the apparently homogeneous 
