476 THEOPHILUS S. PAINTER 



movement occurs is extremely variable and depends apparently 

 on certain changes in the aster and chromosomes. If monaster 

 eggs alone were to be considered, this objection might be met 

 by assuming that the aster exercised a retarding influence on 

 diffusion, but in those eggs treated with phenyl methane, in 

 the absence of asters, the division of the egg was retarded until 

 after the chromosomes had split. 



Further speculation of the subject is not desirable until we 

 have more data upon which to go. The one outstanding fact 

 is that there is a second factor entering into the cleavage of the 

 sea urchin egg, a factor (or set of factors) characterized by a 

 swelling of the ectoplasmic layer, great changes in the surface 

 tension of the protoplasm, and a flow of the .pigment towards 

 the cleavage plane. 



Is this second factor, which the monaster and narcotized 

 eggs lead us to assume, something new? The answer is clearly 

 in the negative. The monaster and narcotized eggs only allow 

 us to see far more clearly the expression of this second force than 

 normal eggs do, and furthermore, permit us to harmonize the 

 widely differing views of other investigators. 



As long ago as 1876 Butschli gave a mechanical theory of 

 cell division based on movements of the protoplasm, and since 

 that time a number of authors have observed movements to- 

 wards the cleavage plane, which might be of significance in 

 cell division. Most conspicuous of these are the observations 

 of Erlanger ('97) who studied living nematod eggs at Butschli's 

 suggestion, (see Butschli '00) and the works of Conklin, who 

 finds in "the vortical flow of cell substance" (Karyokinesis 

 and Cytokinesis, p. 100) one of the most important factors in 

 cell division. 



From a different standpoint we have Loeb's ('95) suggestion: 



Ich stelle mir nun vor, dass an der Oberflache des Eies, moglicher- 

 weise in domjenigen Meridian oder Kreise, dessen Ebene die beiden 

 Strahlensysteme der Centrosome von einander trennt, sobald die 

 Kerntheilung physikalisch abgelaufen ist, Ausbreitungserscheinungen 

 stattfinden. Dieselben fiihren zur Bildung von in Bezug auf diese 

 Ebene symmetrischen Wirbelbewegungen. 



