KEIMBAHN-DETERMINANTS 237 
species whose eggs undergo total cleavage they are, 
under normal conditions, segregated in one definite 
blastomere from the two-cell stage up to the thirty- 
two-cell stage, as a rule, and are then distributed 
among the descendants of the single primordial 
germ cell. In Ascaris it is normally the cell at the 
posterior (vegetative) pole that fails to undergo 
the diminution process. It seems therefore that 
there must be some mechanism in the egg which 
definitely localizes the keimbahn-determinants. 
The segregation of these substances in one blas- 
tomere at the first cleavage division is a result of their 
previous localization, but in later cleavage stages 
events are more difficult to interpret. Both Haecker 
(1897) and Amma (1911) have attempted to explain 
the distribution of the ‘‘Ectosomen”’ in copepods by 
postulating a dissimilar influence of the centrosomes 
resulting in the segregation of these granules at one 
end of the mitotic spindle in the dividing stem cell. 
According to Zeigler’s hypothesis the centrosomes 
during unequal cell divison are heterodynamic, 
and Schonfeld (1901) believes that the synizesis 
stage is due to the attraction of the chromosomes by 
the centrosomes. It is well known that in many 
cases where unequal cell division occurs one aster 
is larger than the other, and this may be the true 
interpretation of the phenomena, but to the writer 
it seems more probable that the entire cell contents 
undergo rearrangement after each cell division, 
possibly under the influence of the material elab- 
orated within the nucleus and set free during mito- 
