PROTOCOCCUS PLUVIALIS. 557 



apparent that the motile form of Eu^lena is constituted 

 on the same type as the primordial cell of the motile form 

 of Protococcus. 



The author then details some observations on the 

 development oiEuglena viridis. 



Uuglena is not always motile ; at certain times it passes 

 into a state of rest. To this end, it assumes a globular 

 form, developes more opaque, denser contents, and forms 

 around itself, a rigid, colourless membrane ; in this state 

 it cannot be distinguished from the still form of Proto- 

 coccus pluvialis, and as in that plant, the cells are often 

 united into floating expansions. In this form, and par- 

 ticularly vphen aggregated into these expansions, it has 

 already been occasionally placed among the Algse ; Micro- 

 cystis Noliii, Kg. appears to be the still form of Euglena 

 sanguinea, and M. olivacea, Kg. is probably to be referred 

 to Euglena viridis. 



This stage, however, of the so-called process of 

 becoming encysted, is not, as commonly supposed, 

 connected with the decease of the organism, but within 

 the membrane, segmentation goes on ; the coloured, 

 enclosed globular body subdividing exactly as in Proto- 

 coccus into two, four, eight, sixteen, thirty-two, or more 

 portions. These isolated, primordial cells, as they may be 

 called, become free, by rupture of the rigid wall enclosing 

 them ; and either resemble their parent, or when much 

 smaller, are very dissimilar to it, assuming more the ap- 

 pearance of green, eyeless Monads. 



On the other hand, the motile form of Euglena, also, 

 just like the motile zoospore of Protococcus may sub- 

 divide into two, or it may be into more, also motile 

 secondary individuals. Whence it is manifest that the 

 development of Euglena viridis, proceeds on precisely 

 the same type as that of Protococcus pluvialis. 



With respect to the motion of the Protococcus cells ; 

 it is to be noticed that Ehrenberg, and with him all 

 later observers, agree that animal motion is voluntary, 

 arising from internal psychical causes, that it is conscious 



