EMBRYOLOGICAL STUDIES WITH THE CENTRIFUGE 



GEORGINA B. SPOONER 



Leland Stanford University, California 



THIRTEEN FIGURES 



The following experiments with Cyclops fimbriatus were begun 

 at Columbia University in the spring of 1908 and those with 

 Arbacia, at Wood's Hole in the summer of 1909. In respect to 

 stratification of materials, direction of cleavage and develop- 

 ment of normal embryos from centrifuged eggs Cyclops gave 

 essentially the same results as others had obtained with Arbacia, 

 The materials of the centrifuged eggs are separated into three 

 layers, oil, protoplasm and yolk. Normal embryos develop from 

 the eggs, whether centrifuged at the stage when the segmentation 

 nucleus is present or after the cleavage spindle has formed. The 

 eggs do not orient themselves in the machine, nevertheless the 

 first cleavage is always perpendicular to the induced stratifica- 

 tion. An examination showed that the segmentation nucleus is 

 easily driven into the protoplasmic band and that the cleavage 

 spindle may also be driven into the protoplasmic layer at any 

 stage in its development but it takes a stronger force to displace 

 the spindle than to drive the segmentation nucleus. The mate- 

 rials of the egg also are harder to separate by centrifuging as the 

 time of first cleavage approaches. There is apparently some 

 increased tension in the egg substance but the karyokinetic fig- 

 ure is not so rigid as to be prevented from its normal functioning 

 by the rearrangement of the materials of the egg. 



Some light was thrown on the structure of the karyokinetic 

 figure by the experiments upon Cyclops. The chromosomes, 

 spindle fibers and the centers of the asters together comprise a 

 unit system which bends, but is not torn apart, by the passage 



