14 Mr ffickson, On the fragmentation [Nov. 14, 



centrosomata, notwithstanding the fact that my material is ex- 

 cellently well preserved. 



The next stage is one in which I have failed to find any trace 

 of a merabrana limitans to the egg nucleus: the protoplasm is, 

 from the manner in which it stains, obviously being distributed 

 through the outer pole of the ovum. Extremely minute granules 

 deeply stained in haemotoxylin or carmine can be seen, but no 

 large chromatin rods, nor asters, nor an equatorial plate of any 

 kind or description can be discovered. 



During the course of the investigation I failed to find any 

 traces of karyokinetic figures in the first divisions of the oosperm 

 nucleus. Thinking that perhaps this failure was due to imperfect 

 methods of staining my preparations, I refrained from publishing 

 my results until I had experimented with a great many different 

 reagents and combinations of reagents. No new results were 

 however forthcoming, and it seems to me to be possible that 

 karyokinesis — in the ordinary sense of the word — does not occur 

 and that the division of the oosperm nucleus is a true amitotic 

 fragmentation. 



It is probable too that this is not the only instance of amitotic 

 division of the oosperm nucleus. 



I should point out that neither Balfour nor any of those who 

 preceded him wei^e able to distinguish any karyokinetic figures in 

 the earliest stages of the segmentation of the Elasmobranchs, 

 although at a later stage he found typical spindles in the blas- 

 toderm. 



More recently Kastschenko has very carefully reinvestigated 

 these early stages with the help of our modern knowledge of stains 

 and preservative reagents and again finds no karyokinesis. 



Kastschenko's results seem to me to be particularly interesting 

 and important, because there can be no doubt ihat his work was 

 very carefully done, that his material was well preserved and that 

 his staining methods were suitable for bringing out the karyokinetic 

 figures. 



He shows very clearly that the so-called yolk nuclei do not 

 arise during and in consequence of the segmentation, but before 

 segmentation and probably in consequence of the repeated divisions 

 of the oosperm nucleus which precedes the division of the egg. 



He further shows that regular segmentation of the agg does 

 not exist in the Elasmobranchs. Only in rare cases could he 

 observe the first segmentation furrow alone. In most cases 

 numerous segmentation furrows appear simultaneously after 

 fertilisation. 



Before segmentation occurs then there is for a very short 

 a true multinucleated plasmodium, the nuclei dividing by karyo- 

 kinesis. 



