History oF ARTIFICIAL PARTHENOGENESIS 51 
they suddenly divide. Since cell division follows nuclear divi- 
sion, I concluded that in this experiment nuclear division went 
on in the hypertonic solution, while cell division was stopped. 
I held the loss of water which the egg had suffered in the 
hypertonic solution answerable for the prevention of cell 
division. If the eggs remain too long in the hypertonic solution 
or if its concentration is too high, nuclear division also comes 
to a stop. W. W. Norman! later undertook a histological 
examination of such eggs and confirmed this conclusion. 
I suggested that the hypertonic solution produces a kind 
of “rigor” in the cytoplasm by the withdrawal of water, and 
that in consequence the movements necessary for cell division 
can no longer proceed. If one adds a little more NaCl to the 
sea-water than is absolutely necessary to stop cell division, 
the breaking-up of the nucleus does not take place either, for 
movements of the protoplasm are very probably necessary for 
this also. This explains the results of Morgan,’ who repeated 
my experiments, but observed no nuclear division. He found, 
however, as I did, that eggs treated for the same time with 
hypertonic sea-water suddenly divide into several cells about 
ten minutes after they have been returned to normal sea-water. . 
Obviously he was dealing with eggs in which the changes in the 
nucleus necessary for segmentation had all taken place, but in 
which the movements of the protoplasm necessary for the pulling 
apart of the chromosomes had been suppressed. Morgan 
observed, however, that the astrospheres were formed in these 
eggs.® 
At the same time Mead also, independently of Morgan, and 
from another point of view, attacked experimentally the 
question of the importance of the centrosomes. Boveri had 
put forward the view that the unfertilized egg is unable to 
1 Norman, Archiv f. Entwicklungsmechanik, III, 106, 1896. 
2Morgan, Anat. Anzeiger, 1X, 149, 1894. 
3 Morgan, ‘‘ The Production of Artificial Astrospheres,”’ Archiv f. Entwicklungs- 
mechanik, III, 339, 1896. 
