646 SCIENCE PROGRESS 



take place, as far as we can see under the microscope, in the 

 cytoplasm. The process by which the nucleoli are extruded is 

 such that the cytoplasmic substance which is capable of dis- 

 integrating organic matter does not get access to the nuclear 

 substance. It appears not improbable that the differentiation 

 into nucleus and cytoplasm is a definite separation of different 

 functions of the cell into different areas, just as the functions of 

 the liver and kidneys are a localisation of certain functions in 

 different areas of the body and different groups of cells. Both 

 are the outcome of more primitive conditions. 



If these arguments are valid, then a differentiation into 

 nucleus and cytoplasm is not essential to life. All that appears 

 to be necessary is certain centres of activity existing in what 

 is apparently the only suitable medium — protoplasm. 



This very vague statement takes us no further without some 

 enlargement. We have good evidence that there may be in cells 

 actual centres of activity of the most fundamental importance 

 which have no apparent morphological structure and can, in 

 fact, only be demonstrated indirectly. We saw, when con- 

 sidering the phenomena of cell division, that the centrosomes 

 formed the centres of two sets of radiations, the which radia- 

 tions formed the spindle fibres to which the chromosomes 

 became attached, the centrosomes forming the poles of the 

 division figure. No one who has studied cell division at all 

 adequately can have any doubt but that the centrosomes are the 

 centres of that energy which produces cell division. Yet in 

 the cells of the higher plants there are no centrosomes ! The 

 radiations appear and form the spindle. The process of division 

 is precisely the same as in other cells but at the centres of the 

 radiations are apparently structureless spaces. Within these 

 structureless spaces must be the centres of energy. We may, 

 1 think, be sure that the chromosomes or collections of chromatin, 

 the nucleus when it exists and the chondriosomes must be 

 surrounded by a membrane which is impermeable to certain 

 substances and it is probable that this membrane is composed 

 of linin ; but what the most primitive state of these structures 

 may be we do not at present know. 



What have we left which is absolutely necessary in the 

 constitution of living matter ? A complex substance composed 

 of carbon, oxygen, nitrogen, hydrogen, phosphorus and 

 sulphur, in which there must be centres of certain kinds of 



