GERM CELLS IN THE ARTHROPODA 173 
Bigelow (1902) has described in Lepas anatifera 
and L. fascicularis certain stages which may bring 
the forms in which no early segregation of the germ 
cells has been discovered into line with the apparently 
more determinate species. In Lepas the yolk, 
which at first is evenly distributed within the egg, 
passes to the vegetative pole and becomes segregated 
in one of the first two cleavage cells (cd?). At the 
16-cell stage the yolk lies within the single entoblast 
cell (d°1), which occupies a position corresponding to 
that of the primordial germ cell in Joina. In this 
connection may be mentioned the fact that in many 
animals the germ cells are supposed to come from the 
entoderm and are characterized by the possession 
of much yolk. 
