CENTRIFUGAL FORCE ON EGGS OF CREPIDULA 337 



was an equatorial one. The internal organization which de- 

 termines the position of spindles and the size and position of 

 daughter cells is still present and active, however much it may 

 have been distorted or disturbed. 



But although this organization persists in centrifuged eggs, it 

 does not persist as a constant structure which is unaffected by the 

 manner in which it is cut by successive cleavages. If the organi- 

 zation of the egg were antecedent to the cleavage and were in 

 nowise changed by the way in which it is cut by the cleavage 

 furrows, the cell which is formed below the equator should give 

 rise to no ectomeres and the one above the equator should pro- 

 duce all of the ectomeres, and all of these should lie at the ani- 

 mal pole. But this does not happen, the cell below the equator 

 gives rise to its normal number of ectomeres just as the one 

 above the equator does. The dislocation of the first or second 

 cleavage does not change the differential character of the follow- 

 ing cleavages. 



2. Results of centrifuging during resting stages between first and 

 second and second and third cleavages (figs. 83 to 92, 95, 96) 



All cell constituents may be dislocated more readily by cen- 

 trifugal force during periods of interkinesis than during mitosis, 

 consequently when eggs are centrifuged in resting stages be- 

 tween cleavages, not only are yolk and cytoplasm displaced, 

 but also nuclei and centrospheres. In figures 83 to 92 are shown 

 eggs which were centrifuged in various axes in the 2-cell stage; 

 figures 95 and 96 were centrifuged in different axes in the 4-cell 

 stage. The polar bodies mark the animal pole and in every egg 

 shown the different cell constituents are more or less displaced 

 from their normal positions. But the manner of this displace- 

 ment shows clearly that these constituents are not free to 

 stratify according to their specific weights. While the major 

 portion of the yolk goes to the centrifugal pole and of cytopalsm 

 to the centripetal pole the boundary between these is not a 

 plane surface, but there are 'lanes' or projections of cytoplasm 

 which remain connected with the animal pole even though most 



THE JOURNAL OF EXPERIMEXTAL ZOOLOGY, VOL. 22, NO. 2 , 



