13 W. Hofnieister on the Propagation 



From the half-shells of cells of the same Docidium which 

 dehisced under the eye of the observer, emerged, within half-an- 

 hour, to the extent of ith or jth of the length of the half-shells, 

 the daughter- cells, still intimately connected at the point of 

 contact. They could henceforth be perceived to be enclosed by 

 a cellulose coat, firm although delicate. Treated with reagents 

 strongly extracting water, such as glycerine, one or both of the 

 extruded pieces frequently drew back into the halves of the shells 

 of the mother-cell^ the projecting pieces of membrane becoming- 

 doubled inwards (fig. 24). The just-emerged coats of the 

 daughter-cells of Docidium did not take a blue colour when 

 treated with iodized chloride of zinc, while the old halves of the 

 membrane of the divided cell assumed the blue colour im- 

 mediately. 



In Cosmarium margaritifei'um (figs. 29, 30) and Staurastrum 

 dejectum, it may be easily observed that a slight elongation of 

 the isthmus, and the formation of a septum passing across the 

 middle of this, precedes the appearance of new half-cells in the 

 deep constriction. It is after the appearance of the septum that 

 the old wall of the mother-cell breaks by an annular fissure 

 exactly at the place where that septum is formed. The two 

 halves of the old cell-coat are then separated by the bulging-out 

 of the younger, inner layers of membrane, not firmly adherent 

 to the old portions. The new halves are at first lined only by 

 protruded portions of the pellicle of their contents (outermost 

 layer of the parietal coats of protoplasm) belonging to the older 

 half-cells ; from the moment only of the dehiscence of the old 

 cell-coat, does a portion of the granular contents of the older 

 cell-halves make its way into the new emerging halves. 



In like manner, doubtless, occurs the cell-division of Mi- 

 crasteiias, of the large forms of Euastrum, Cosmarium, Staur- 

 astrum, and other Desmidiese, only that they have not been ob- 

 served completely, because these larger Desmidieje very seldom 

 multij^ly by division out of the natural stations. The cell-divi- 

 sion of the Diatomese that have hitherto been observed in vege- 

 tative multiplication, diflers in essential points from that just 

 described. 



When a cell of Navicula (Pinnularia) viridis is about to divide, 

 there appears upon one of the secondary sides (front view of 

 English authors), parallel to the primary sides (the furrowed 

 faces of the cell having an elongated elliptical outline), an 

 annular rim, which, growing gradually inwards, consti'icts the 

 contents of the cell by an annular furrow, in a manner 

 exactly similar to that of the commencement of cross-division 

 in a cell of Cladophora. When a cell in this state is treated 

 with substances producing slight endosmosis (for instance, a 



