552 CELL DIVISION IN EGGS OF CREPIDULA. 



On the other hand this view is contested by Boveri (1907) and Strasburger (1908) 

 on general grounds and is not confirmed by the observations of Richards (1909, 

 1911), nor by the experiments of Hacker (1900) and Schiller (1909) on Cyclops 

 eggs subjected to ether, nor by the experiments of Nemec (1903), who repeated 

 the work of Wasielewski (1902, 1903) on root tips of Vicia subjected to chloral 

 hydrate, and reached the conclusion that the supposed amitoses have arisen 

 through the transformation of normal mitotic figures. 



On the other hand R. Hertwig (1898), Herbst (1909), Godlewski (1909), 

 Konopacki (1911), Lang (1901), Calkins (1901) hold that there is no principal 

 distinction between mitosis and amitosis and that they may both occur without 

 interference with normal processes of reproduction and differentiation. 



So far as concerns many of the observations and experiments named it must 

 be admitted that they are not critically conclusive; either it is not shown beyond 

 question that the divisions are genuine amitoses, or it has not been proved that 

 the cells are normally differentiating embryonic cells. In particular most if not 

 all of the figures given by Child, Hargitt, Patterson, Glaser and Gurwitsch may 

 be duplicated by figures in which it is known that division is by mitosis. The 

 wholly or partially distinct nuclear vesicles may be fusing rather than sepa- 

 rating, and such is undoubtedly the case in my experiments. Godlewski recog- 

 nizes the difficulty of distinguishing the fusions of karyomeres from direct 

 nuclear divisions, but in my experiments this distinction can be made with 

 certainty, not only because every stage in the formation and fusion of karyo- 

 meres may be seen in the division of a particular cell, but also because the rela- 

 tive stages of karyomeres in the division cycle can be distinguished by the 

 character of the chromatin, and the fusions are always more complete in the 

 later than in the earlier stages. 



A further matter to which I believe attention has not hitherto been called 

 is that the scattering of chromosomes along the length of the spindle leads to 

 the formation of chromatic connections between daughter nuclei in the rest- 

 ing stage. Such chromatic connections have hitherto been accepted as un- 

 doubted proof of amitosis, and Godlewski in his review, after dismissing many 

 other more or less doubtful cases, bases his conclusion that amitosis may occur 

 in normally differentiating tissue upon the undoubted cases given in the works 

 of Gurwitsch and Nathansohn. I am unable to speak from personal experi- 

 ence of the results obtained by the last named investigator in his experiments 

 on Spirogyra, but the figure given by Gurwitsch of a mitotic division following 

 an amitotic one in a blastomere of a centrifuged Triton egg, cannot go unques- 

 tioned. The chromatic connection between the two nuclei shown, is no evidence 

 of amitosis, but rather of the scattering of chromosomes along the spindle, at 

 the previous division of these ceUs. I have repeatedly observed such scattered 

 chromosomes and the resulting chromatic connections between daughter 

 nuclei, in practically all of my experiments, though they are figured chiefly 

 in eggs subjected to diluted sea water; they also occur in centrifuged eggs, as I 

 shall show in a later paper. 



