442 L. V. HEILBRUNN 



15 minutes. The increased^ viscosity of the egg during this 

 amphiaster stage could be more easily demonstrated by the needle 

 in the eggs of Echinarachnius and Cerebratulus than in those 

 of Arbacia. 



''After completion of the cleavage process, there are indica- 

 tions that the firmness of the cytoplasm persists in the two blas- 

 tomeres while they are still more or less spherical." 



These remarks of Chambers apparently apply to the sea- 

 urchin egg. Working on the same egg apparently without any 

 knowledge of Chambers' 1919 paper, to which he does not 

 refer, Seifriz ('20) finds : ' ' With the first appearance of the amphi- 

 asters there is a pronounced decrease^ in viscosity of the central 

 region of the cell, and this condition is maintained throughout 

 the intermediate stages of divisions (from middle prophase to 

 late anaphase)." Later he says, 'Svith the completion of divi- 

 sion we have in each daughter cell of the embryo a general pro- 

 toplasmic consistency identical with that of the egg before 

 fertiUzation. " 



Thus Chambers considers the amphiaster stage to involve 

 increased viscosity and Seifriz regards it as involving a pro- 

 nounced decrease in viscosity (at least of the central region). 

 And whereas, after the first cleavage, Chambers finds high vis- 

 cosity, Seifriz finds a viscosity identical with that of the unfer- 

 tilized egg. It might be thought that the difference is due to a 

 difference in the capability of the two investigators, but this 

 does not appear to be the case. For whereas Seifriz is wholly 

 wrong in stating that the viscosity just after cleavage is no 

 greater than in the unfertilized egg, Chambers is equally wrong 

 in stating that the amphiaster stage is a stage of high viscos- 

 ity. Evidently the difficulty lies primarily with the method. No 

 doubt it is too subjective. Apparently all evidence as to pro- 

 toplasmic viscosity gained from microdissection should for the 

 present at least be regarded as merely suggestive. 



In this paper it has been sho^vn that during mitosis viscosity 

 changes occur in Cumingia and Nereis which are similar to those 



° Italics mine. 



