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 puUing 

 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 unfertihzed egg is unable to 



1 Norman, Archiv f. Entwicklungsmechanik, III, 106, 1896. 



2 Morgan, Anat. Anzeiger, IX, 149, 1894. 



' Morgan, " The Production of Artificial Astrospheres," Archiv f. Entwicklungs- 

 mechanik, III, 339, 1896. 



