PROTOCOCCUS PLUVIALIS. 543 



There is a large number of different modes of propaga- 

 tion in Protococcus pluvialis, which, indeed, are all 

 fundamentally analogous, but produce very different forms. 



The main distinction depends upon the number of 

 divisional individuals produced from a parent-cell. Their 

 number appears always to be a sub-multiple of 2. A 

 cell may produce 2, 4, 8, 16, 32, 64 individuals. 



The propagation depends upon a division of the cell- 

 contents, particularly of the colourless or coloured pro- 

 toplasm, or of the primordial sac. This body, without 

 any demonstrable influence of a nucleus, is capable of 

 subdividing into a determinate number of portions, in 

 the ratio just stated. Each of these portions acquires a 

 globular figure, in the next place surrounds itself with an 

 envelope of protoplasm, and then represents a visible 

 organism, which, after the resorption of the parent cell- 

 membrane, is capable of existence as an independent 

 reproductive individual. 



The protoplasm which constitutes the external boun- 

 dary of' this body, like all organised protoplasm, is 

 capable of secreting a rigid vegetable cell-membrane. 

 Two conditions now may present themselves. 



1. Either, such a rigid, ligneous membrane is formed 

 within the mother-cell, around the portions of proto- 

 plasm separated by division as above, that is the pri- 

 mordial sacs : in which case there are produced only 

 still secondary cells, usually different in their structure 

 from the parent-cell. This process takes place only when 

 the parent-cell itself belongs to the still form, that is to 

 say, when the cell-contents or the primordial sac are closely 

 surrounded by a rigid, tough, Hgneous membrane : 



2. Or, the secondary individual, surrounded only by 

 a tunic of protoplasm, is liberated in this condition as a 

 primordial cell, and developes two vibratile filaments; 

 it then has the faculty of motion, and represents a naked 

 zoospore. This process may take place as well in the 

 segmentation of still, as of motile primary cells. Here, 

 also, two conditions are possible. 



