dr. XII] INTERPRETATIONS AND CONCLUSIONS 129 



period, so that a qualitative division of the nucleus may result 

 different from the corresponding normal qualitative division. 

 The second cleavage, for instance, may come first (qualitatively) 

 as a result of the position of the nucleus in the protoplasm. 



Roux further suggested that the consecutive series of nuclear 

 divisions must be different in kind in the normal and in the 

 compressed eggs, and that an " anachronism " has taken place 

 in the latter case. By this " anachronism " Roux has tried to 

 save his theory of qualitative division of the nucleus during 

 the cleavage-period. 



To sum up Roux's later position, we may say that in order 

 to vindicate his earlier theory of a qualitative division of the 

 nucleus and a resulting self-differentiation of the first-formed 

 blastomeres, he has been obliged in the first place to bring for- 

 ward his theory of postgeneration, assuming that along with the 

 qualitative division of the nucleus a parallel quantitative divi- 

 sion of the germ-material also occurs. Further, Roux assumes 

 that the kind of qualitative division of the nucleus is directly 

 influenced by the arrangement of the protoplasm, and, as we 

 have seen above, he is unable to explain satisfactorily the 

 results of the experiment of the compressed egg, except as an 

 "anachronism." These complications into which Roux has 

 been forced are largely the outcome of the primary assump- 

 tion of a qualitative division of the nucleus. This Roux-Weis- 

 mann hypothesis of qualitative nuclear division has, however, 

 no known histological facts in its favor. On the contrary, all 

 we know of nuclear divisions speaks clearly in favor of an exact 

 division of the chromatin-material, and a most elaborate mech- 

 anism is present to bring about this result. 



EXPERIMENTS ON OTHER FORMS 



The results obtained from a study of the development of 

 fragments of the unsegmented egg and of isolated blastomeres 

 of ctenophors 1 have a direct bearing on our interpretation of the 

 experiments on the frog's egg. When the first two blastomeres 

 are separated from each other by a sharp needle or cut apart by 

 a pair of small scissors, each continues to cleave as a half, i.e. 



1 Chun ('92). Driesch and Morgan ('95). 



