Vol. XVII. July, 1909. No. 2. 



BIOLOGICAL BULLETIN 



KARYOKINETIC FIGURES OF CENTRIFUGED EGGS. 



AN EXPERIMENTAL TEST OF THE CENTER 



OF FORCE HYPOTHESIS. 



FRANK R. LILLIE. 



In the annelid Chtftoptents the first maturation spindle forms 

 in the unfertilized eggs after they are shed in the sea-water, and 

 develops to the stage of the mesophase (Fig. i). Here it remains 

 standing without change, it may be for hours, unless the egg be 

 fertilized or otherwise effectively stimulated. The eggs can be 

 obtained at Woods Hole in unlimited amounts for a period of 

 about two months during the summer, and as they may be taken 

 from the worms at any time of day they furnish ideal material. 

 The possibility of experimenting directly on a definite stage of 

 the karyokinetic figure is naturally suggested by the material 

 itself, and I propose to give here an account of the results of 

 experiments with centrifugal force, which have been carried on 

 during four successive seasons, so far as they are related to the 

 karyokinetic figure. A communication of the results was made 

 before the joint session of the Central Branch of the American 

 Society of Zoologists and Section F (Zoology) of the American 

 Association for the Advancement of Science held in Chicago, 

 December, 1907, and an abstract was printed in Science, N. S., 

 Volume XXVII., pp. 907-908, June 12, 1908. 



The principal advantage of this material, aside from its availa- 

 bility and abundance, is that it offers the rare opportunity of 

 experimenting on a definite and fixed stage of the karyokinetic 

 figure. At the stage in question the forces concerned in karyo- 

 kinesis have reached a certain balance which is maintained in- 

 definitely, until the equilibrium is upset by the conditions initiated 

 by entrance of the spermatozoon or some other effective change. 



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