132 Historical and Critical Considerations 



For these reasons I believe that a critical review of our 

 knowledge in this field will be of substantial usefulness. 

 It will then be shown how, in almost all cases, the attitude 

 of the plasmatic membrane and of the granular plasm, 

 during cell-formation, is in fact unknown. At least in 

 all the cases which seem to contradict the panmeristic con- 

 ception. 



It is not a question of whether this latter conception 

 is correct or not. This seems to me to have been proven 

 above any doubt by the researches of the investigators that 

 have been quoted. The question is whether, with this 

 conception, we are to regard the granular plasm and the 

 limiting membrane as two intrinsically different organs, 

 which pass over into one another as little as the nuclueus 

 and the chromatophores, or whether they stand in a sim- 

 ilar relation to each other as the amyloplasts and the chlo- 

 rophyll-grains. As long as it was thought that the gran- 

 ular plasm had the power of producing the other members 

 by a process of differentiation, it was natural to assume 

 a like mode of origin for the plasmatic membrance. It 

 is therefore not astonishing that, even at present, this 

 view is still regarded as the one that actually obtains. 

 The instance described by Mohl as a type of cell-di- 

 vision, and which involved the historically noteworthy 

 discussions of the question as to whether the ^protoplasmic 

 body played a passive or an active role during this process 

 is well known to all. Like Mohl's type of the filamentous 

 algae, Cladophora, Spirogyra is in more recent times pre- 

 ferred for this study. At the future plane of division 

 the limiting membrane and granular plasm fold into a 

 ring which, growing inwards, apparently simply cuts in 

 two the remaining part of the cell-contents. For the 

 daughter-cells the two new parts of the limiting membrane 



