SPECULATIONS UPON THE ORIGIN OF LIFE 645 



it is quite reasonable to regard bacteria and other uni- 

 cellular forms such as spirochetes, in which the chromatin 

 appears to be excessive in proportion to the whole body, as 

 organisms specially modified from ancestors that were more 

 primitive for particular conditions of life. Moreover, some 

 cytoplasmic structures take basic stains in a manner very 

 similar or identical to the chromatin. 



Perhaps the most important point of all regarding the 

 relations between nucleus and cytoplasm is the fact that we have 

 conditions in which there is no definite nucleus. At certain 

 stages in the life cycles of some organisms the chromatin is 

 distributed throughout the cell. It is probable, personally I 

 feel certain, that these small masses of chromatin are always 

 surrounded by linin but this does not affect my argument. 

 Also, when any cell divides in the manner described above, 

 it is obvious that the ground-substances of the nucleus and 

 of the cytoplasm are inextricably mixed together. Round the 

 chromosomes there is always an envelope of linin and the same 

 or something of a similar nature may possibly exist in the case 

 of the chondriosomes. It is evident that the chromosomes, the 

 chondriosomes and the nucleus must be surrounded by some- 

 thing which is impervious to those substances present in the 

 cell which cause the disintegration of organic matter. It may 

 well be that this is a property of linin. 



It therefore seems to me clear that a differentiation into 

 nucleus and cytoplasm is probably not indispensable for the 

 life of all cells. It would appear rather to be a differentia- 

 tion which has been brought about by natural selection from a 

 more primitive condition. This differentiation disappears 

 temporarily during division in all cells. Except during 

 division, an exchange of substance takes place between nucleus 

 and cytoplasm through the extrusion of the nucleoli. When 

 the cell is in a vegetative condition the nucleoli multiply con- 

 tinually and are extruded from the nucleus. The nuclear 

 membrane is pushed out in front of the migrating nucleolus and 

 closes up behind it as it passes. The staining reaction of the 

 nucleolus changes directly it reaches the cytoplasm. 1 All 

 processes of digestion, absorption and of specific secretion, 



1 Walker, C. E., and Francis M. Tozer, "Observations on the History and 

 possible Function of the Nucleoli in the Vegetative Cells of various Animals 

 and Plants," Quart. Journ. of Exper. Physiology, vol, ii. No. 2, March 1909. 



