234 GERM-CELL CYCLE IN ANIMALS 



plasm" of Cynthia to be crowded with plasmosomes, 

 differing in this respect from other ^gg 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 role 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. 



