THE DIVIDING CELL 347 



free at last to discede from its sister. We have here the experi- 

 mental demonstration of the fact that the chromosomes are 

 "mitokinetised" by induction in the place they occupy in the 

 cell-field, and that this will account for the completion of their 

 splitting and final discession, because they are composed of 

 a substance more permeable to mitokinetism than any other 

 element of the cell. We are perhaps justified in conjecturing, 

 as I did nine years ago, that this susceptibility to mitokinetism 

 is the function of the actual chromatic substance, which augments 

 so enormously on the approach of nuclear division, and which 

 diminishes during the intermediate periods of ordinary cell life : 

 thus the important structures of permanent morphological value 

 of the chromosome would be the achromatic substance, and the 

 function of the chromatin would be mainly mechanical, sub- 

 serving the partitive division in mitotic division. This view 

 has since received independent advocacy from Boveri. I shall 

 discuss it more fully in the Rivista di Scienza. 



But in the cell there is one essential point of difference from 

 the conditions in our models : the more permeable substance is 

 not merely precipitated from the medium once and for all ; it 

 grows at the expense of other substances in the cell. This is 

 especially evident in the segmenting egg, with its enormous 

 supplies of not-living food material. The different character of 

 this permeable material of the cell-chains has long been recog- 

 nised, and its function denoted by the terms " archoplasm " 

 (Boveri) and "kinoplasm" (Strasburger), which have been 

 applied to it. From the consideration of the work of Vejdowsky 

 and Mrazek, it would almost seem certain that the centrosomes, 

 so conspicuous in the animal cell, have for their chief function 

 the metabolic processes that determine this growth. 



In Metaphytes the centrosomes are, if present at all, ex- 

 ceedingly minute ; and Anstruther A. Lawson has shown that 

 the spindle-fibres take origin immediately in contact with the 

 nuclear wall and extend thence into the cytoplasm, only slowly 

 assuming the spindle-grouping. We may infer that the meta- 

 bolic function of forming the kinoplasm lies in the centrosome in 

 Metazoa and in the nucleus in Plants. As stated just now, the 

 limiting membrane of nucleus and of centrosome behaves as 

 if infinitely permeable to mitokinetism, and affords a perfect 

 screen to its contained plasmatic structures ; for these are as 

 free from mitokinetic strain as would be the contents of a metal 



