538 THE NATURAL HISTORY OF 



toeoccus cell which is alike in any two individuals being 

 the enveloping cell. 



The anterior projection, beak or rostellum, is always an 

 immediate prolongation of the colourless protoplasm, 

 forming the outermost boundary of the primordial cell, 

 but into which, speaking generally, the coloured sub- 

 stance is not continued. 



The contractile movements of the primordial cells is 

 usually very slow, but occasionally more rapid, in that case 

 very closely resembling those of Euglena viridis. These 

 more rapid changes of figure and appearance, take place 

 particularly upon the partial evaporation of the water in 

 which the cells are contained. But if this evaporation 

 proceed further, and fresh water be not added, further 

 and more important changes take place in the primor- 

 dial cells of Protococcus pluvialis, which may be com- 

 prehended under the term of "deliquescence" This 

 process is exclusively characteristic of the vegetable 

 primordial cell, particularly in all zoospores on the one 

 side, and also in the Infusoria on the other. 



The phenomena in question present two stages or 

 phases. In the first, the outlines appear less sharply 

 defined, because the coloured substance is somewhat 

 retracted from the border of the primordial cell. It 

 is then clearly evident that the colourless protoplasm 

 constitutes the special smooth boundary membrane of 

 the primordial cell. The cells become flattened, and at 

 the same time wider. The contents also are now 

 altered ; previously more homogeneous and transparent, 

 they now become throughout granular, and the red sub- 

 stance runs together into large drops. At this time 

 commences the formation of vacuoles, the number of 

 which continues to increase. In this way the interior of 

 the primordial cell again becomes colourless, clear as 

 water, and the granular, coloured contents, compressed 

 against the walls. The figure of the cell, in the mean- 

 while, is so much expanded that it comes to be applied 

 upon the wall of the enveloping cell, ultimately filling it 



