no SCIENCE PROGRESS. 



Bacterolds, has been frequently demonstrated in animal 

 and vegetable cells, and Biitschli points out that granules 

 similar in appearance to bacteroids occur in the Vorticellinse 

 and may be observed at certain times to be in a state of 

 rapid proliferation. 



Just before writing these pages I have been shown 

 preparations exhibiting the numerous bacteria symbiotic 

 in Pelomyxa, and it is very possible that the rapid 

 proliferation of bacteroids has been mistaken by various 

 observers for the reproductive activity of granules forming 

 an integral part of the cell. It is almost certain that the 

 mistake has been made in some cases, and until further 

 investigation has increased our knowledge of the various 

 micro-organisms which are symbiotic or parasitic in cells, it 

 is well to be somewhat sceptical of statements regarding 

 the divisional processes of cell contents. It would seem then 

 that our present knowledge does not justify our regarding 

 all the particles of a cell as originating in a similar manner 

 from the division of pre-existent similar particles, though 

 we must affirm in the most positive manner that some few 

 of the constituents of the cell originate in this way only, and 

 are never produced de novo. The question now to be 

 considered is this : must we, because these bodies (the 

 centrosomes, chromosomes, etc.) assimilate, grow and 

 reproduce themselves by division, regard them as indepen- 

 dent vital units? A cell exhibits these phenomena and the 

 cell is regarded as an independent unit in posse, if not 

 actually in esse ; must we therefore attribute to all bodies 

 exhibiting the same phenomena the character of indepen- 

 dent units ? The answer, I believe, is very decidedly no. 

 Cells would never have been regarded as independent units 

 if they had merely been observed to assimilate, grow and 

 divide, whilst retaining their connection with other cells 

 undergoing the same processes. The quotations which 

 I have given from Schwann's work show that the 

 theory that the cell is an independent life unit was not 

 founded on the fact that it assimilates, grows and divides, — 

 Schwann indeed overlooked the phenomena of reproduction 

 by division — but upon the fact that cells are capable of 



