132 



Scientific Proceedings (38). 



82 (492) 



Experiments bearing on the nature of the karyokinetic figure. 



By T. H. MORGAN. 



In the three following ways the results of centrifuging the egg 

 of Cerebratulns throw light on the nature of the karyokinetic 

 figure. 



1. If the egg is centrifuged when the polar spindle is present, 

 the spindle may be carried bodily, without injury to its rays, to 

 the center of the egg, in those cases where the yolk is driven into 

 the region occupied by the polar spindle. If the centrosomes are 

 centers of force, we must suppose that these centers produced at 

 each state in the migration of the spindle new rays and a new 

 spindle. This seems highly improbable when the time usually 

 taken for the formation of the rays is considered. The same 

 reasoning applied to the central spindle would lead to the con- 

 clusion that its rays, too, are continually reformed during the 

 migration. 



2. When the basic granules of the egg are driven into the 

 region of the segmentation spindle, the granules become arranged 

 along the alveoli through which the rays also pass, and assuming 

 a bead-like arrangement may obscure the rays. Lillie has advanced 

 this evidence as demonstrative of the center of force hypothesis. 

 My observations lead to the opposite conclusion ; for I find no 

 evidence that these granules replace the fibers. Whether the 

 granules by changing their nature become incorporated into the 

 polar rays is another question that must be left open at present, 

 but even if they do so, this does not prove the center of the force 

 hypothesis. 



3. When the asters of the segmentation spindle become 

 attached to the male and female pronuclei, they may be carried 

 to the light pole when their nuclei are transported to that region. 

 The fibers are often thrown into spirals, which fact is difficult to 

 explain on the center of force hypothesis. 



