586 VERA DANCHAKOFF 



shown by the experiments of McClendon. The chromosomes 

 seem to be firmly attached to the spindle since the electric cur- 

 rent compels the whole spindle to move together with the chromo- 

 somes. This is also shown in Hill's work, and that of Conklin 

 and others on centrifuged eggs. The eggs of the sea urchin, 

 during the metaphase, do not present a material particularly 

 favorable for the study of the splitting movements of the chro- 

 mosomes. These are 36 in number, small and compactly drawn 

 together. The data about the further development are not 

 precise enough to allow definite conclusions. 



Similar, but less regular, is the development of chromosomes 

 of the spindle, and centrosomes in artificial parthenogenesis. 

 Parthenogenetic eggs, in which the nucleus has not been damaged 

 by application of too strong solutions, exhibit a regular develop- 

 ment. Even artificial cytasters may disappear, the chromatic 

 substance finding finally an outflow to the nucleus. Absorption 

 of chromatic substance proceeds in the usual way and chromo- 

 somes are differentiated within the nucleus. 



The study of anomalous development of the egg incited by the 

 breaking up of the achromatic nucleus into more or less numer- 

 ous parts is very instructive. The egg presents in this case sev- 

 eral regions of attraction of the chromatic substance. The dif- 

 ferentiation of chromosomes cannot proceed regularly, as shown 

 on figures 20 and 22. This injurious influence of fragmentation 

 of the nucleus on the differentiation of chromosomes indicates 

 how important is the role of the achromatic substance of the 

 nucleus in the differentiation of chromosomes. Yet it seems as 

 if the achromatic nucleus be not capable of forming the chromo- 

 somes by itself. Eggs which do not present the above described 

 dissolution of the chromatic accumulations do not develop. The 

 achromatic nucleus may not present any injury, no chromatin 

 particles are formed within the nucleus. Such eggs can remain 

 in the culture from six to eight hours without showing any 

 morphological changes. 



The differentiation of the chromosomes in the nucleus of 

 parthenogenetic eggs proceeds in a manner similar to that of 

 normal fertilization. The morphological pictures are just as 



