5ii2 THE NATURAL HISTORY OP 



the interior. But in the present case the course of 

 development is completely opposed to this view. 



On the other side, again^, the primordial cell corresponds 

 to the cytoblast of the common plant-cell, not only 

 because, like that, it is free, and for the most part excentric, 

 floating in the interior of the cell, but also in its relation 

 to the development of the cell-membrane, in which it 

 agrees in its function with that assigned by the theory of 

 Sclileiden and Schwann, to the nucleus, in the formation 

 of tlie cell-membrane. 



The form oi Protococcus, named by Flotow Hmn. pluv. 

 versalUis setiger (fig. 15), presents a perfect analogy 

 between the primordial cell and the nucleus of the 

 common plant-cell. He states that the filaments which 

 proceed from the central mass to the peripheric cell-wall, 

 are tubular, giving passage to the red molecules from 

 the central mass. These filaments, however, which pro- 

 ceed from the outer wall of the primordial cell towards 

 the inner surface of the enveloping cell, correspond mor- 

 phologically to the so termed mucous filaments (sap- 

 streams) by which the cytoblasts are coumionly retained 

 in the centre of their cells. Thot they also correspond 

 chemically with these, is proved by the fact that they are 

 rendered more distinct by iodine, and that they can be 

 made to retract by means of reagents ; and, in fact, they 

 exhibit, in the course of development, pecidiarities which 

 characterise them as consisting of protoplasm. 



The existence of these delicate threads passing from 

 the central mass to the enveloping cell, and the appear- 

 ance occasionally of little particles having molecular 

 motion, serve to show that the contents of the enveloping 

 cell are not of a gelatinous consistence, but of an aqueous 

 nature. And the continuity of the primordial cell-wall 

 with the filaments shows that it is surrounded only with 

 a denser layer of protoplasm, and is not enclosed in a 

 rigid membrane of cellulose. 



The form versatilis, therefore, of Prot. pluvialis is 

 to be regarded as a cell with clear aqueous contentSj in 



