i;8 SOME RECENT DEVELOPMENTS 



tained that there is one fundamental form of nuclear 

 division, presenting a series of gradations from the 

 simple direct method described by Remak up to 

 the extreme complication seen in typical cases of 

 mitosis ; and in favour of this view there is a con- 

 siderable amount of evidence already accumulated. 

 Thus Waldeyer himself has shown that if a frog's 

 epidermis, in which mitosis usually occurs, be 

 treated with silver nitrate, direct nuclear division 

 can alone be demonstrated, from which he argues 

 with great justice that the distinction between the 

 two methods may in other cases also be only 

 apparent, and due to the particular mode of histo- 

 logical treatment adopted. Pfitzner has succeeded 

 in staining both the nucleoplasm and chromatin 

 simultaneously, and maintains that mitosis concerns 

 not merely the chromatin but the entire nucleus ; 

 and further that the cell protoplasm takes no part 

 in the process. Btitschli, Hertwig, Schewiakoff, 

 and others have shown that in Protozoa, in which 

 all the phenomena of mitosis occur, the nuclear 

 membrane may remain complete the whole time 

 until the final division of the nucleus into the two 

 daughter-nuclei ; while Boveri and others have 

 found that in segmenting eggs of various animals 

 the various stages of mitosis may sometimes be 

 very clear, and at others very obscure. Finally, 

 Carnoy asserts that mitosis, so far from being a 

 uniform process in all cases, presents so many 

 varieties that no one series can be viewed as essen- 

 tial ; he even denies that the longitudinal splitting 

 of the chromatin threads into sister-threads is uni- 



