234, GERM-CELL CYCLE IN ANIMALS 
plasm” of Cynthia to be crowded with plasmosomes, 
differing in this respect from other egg regions. 
Experiments, especially those of Lillie (1906, 1909), 
Morgan and Spooner (1909), Morgan (1909a), and 
Conklin (1910), have shown that in many eggs the 
shifting of the supposed organ-forming substances 
has no influence upon development, and leads to the 
conclusion that these visible substances play no 
fundamental réle in differentiation, but that the 
invisible ground substance is responsible for de- 
terminate development. The eggs of different ani- 
mals, however, differ both in time and degree of 
organization, and the conflicting results may be 
accounted for by the fact that specification is more 
precocious in some than in others. 
The most plausible conclusions from a considera- 
tion of these observations and experiments are that 
every one of the eggs in which keimbahn-determi- 
nants have been described consists essentially of a 
fundamental ground substance which determines 
the orientation; that the time of appearance of 
keimbahn-determinants depends upon the _ preco- 
ciousness of the egg; that the keimbahn-determi- 
nants are the visible evidences of differentiation in 
the cytoplasm ; and that these differentiated portions 
of the cytoplasm are definitely localized by cytoplas- 
mic movements, especially at about the time of 
maturation. 
